This is my feeling as well. I play (or played) several fretted chromatic instruments. The dulcimer is unique in its diatonic tradition. I find it simple, yet challenging; which in turn provides a refreshing approach to my music. 

That said, I respect others who have personal and valid reasons for choosing to play a chromatic dulcimer.

@Lisa-Golladay 's post covered the practical pros & cons quite well.

Yes, I agree with Jean Ritchie.  For me, the dulcimer is diatonic in nature, anything else is not quite a dulcimer.

I know I'm bringing up an old thread, but - oh well.  I play guitar, clawhammer banjo and am now learning dulcimer.  When I learn a mountain instrument, such as clawhammer banjo or dulcimer, I want to learn and play it the way the the original players played it.  I guess I want to learn the tradition, keep it, and maybe add a personal touch here and there.  But "old school" tradition is very important to me.  So, if I want chromatic, guitar or banjo is the way to go for me. With clawhammer banjo, I thought of transferring it to guitar - but why?  It was made for banjo. With a dulcimer I want that lovely sweet sound of the mountains and to keep the tradition alive as best I can.  I don't want to make them into something modern and into something they are not.  There are plenty of hybrids instruments - banjo dulcimers, guitar banjos, etc. out there if you want to come into the up to date modern world.

So, in my mind, let a guitar be a guitar, let a banjo be a banjo and let a dulcime be a dulcimer.

Every chromatic dulcimer comes with a free diatonic hidden in plain sight. Ignore the extra frets until you need them. For some people this is no problem at all. For others it's confusing and it sounds wrong and they just don't like it. Either opinion is perfectly valid. It's your dulcimer.

I play chromatic. I play diatonic. I play half-breeds with 1.5 and 6.5 frets. Since you asked why NOT buy chromatic, here's what I got:

Chromatic is harder to play. It has wrong notes. This is not insurmountable. Think about the guitar players you know; are they all rocket scientists? If they can manage a chromatic fretboard, so can you. However, if you hate to practice scales you will probably be happier with a diatonic.

Noter speed bumps. Do you play with a noter? Can't stand the idea of your dulcimer sounding like a slide guitar? This is a dealbreaker for some. And some could not care less. Know thyself.

Lack of instructional materials. This is a big one. There are a few books and videos for learning chromatic dulcimer, but not nearly as many resources as diatonic. When an absolute beginner asks me about dulcimers, I usually steer them toward diatonic.

Modal scales get difficult. Dorian is my favorite mode for improvising, and it's so easy on a diatonic! Dial in the right tuning and off you go. Whereas learning all the scales on chromatic is a major learning curve.

Other dulcimer players fly into a panic. Seriously. A friend gets a dulcimer and wants to play together. Bring out a chromatic and they'll yelp in terror. It doesn't look the same. It's too complicated! I have to keep a diatonic around or I won't have any dulcimer friends.

It's not traditional. This matters to many people. And sometimes (living history events? tapping into your personal memories of dulcimers past?) it may matter to you. If the sound you fell in love with is the sound of a traditional silvery noter/drone modal dulcimer, a chromatic is unnecessary and will make it harder to replicate that old-time sound.

That said, if you already have a diatonic dulcimer and you're considering chromatic, and if you have the time and inclination to learn something new, then my advice is go for it.

A couple of other points I forgot, a chromatic will probably be a bit more expensive to buy and much harder to sell.

Both Ken and Robin are correct.

Your instrument is personal.

As Jerry Rockwell says: It’s a possibility box.

Look at lots of video clips of folks playing a variety of music on a variety of different fretted dulcimer configurations and, perhaps, that will give you an idea of what approach you'd like to take to making music.  First and foremost, lean into what music is in your heart to make and get the tool (instrument) with which to do it best.  It's a process and it can be lots of fun to explore.  

TRADITION! 

When asked about dulcimer with “extra" frets, Jean Ritchie replied “In a strict sense it has a different finger board, it’s not quite a dulcimer anymore.”    

You can find all the notes in the dulcimer's range, but you have to be willing to re-tune at least one string to do so (takes less than 30 seconds, with practice).

If you want a chromatic instrument lay a guitar on your lap and play that.  Or I can build you an  "acoustic lap guitar". Just don't call it a dulcimer.   Part of the essential definition of Dulcimer, to many of us, is the diatonic fretboard.

If you are playing mostly "classic dulcimer songs" especially from tabulature rather than SMN, it will be 'more difficult' because the fret numbering convention is different, and you'll have to find the fewer diatonic frets among the plethora of chromatic frets.  You won't be able to simply count 1,2,3,4... to find a tab numbered fret.  With a chromatic instrument that becomes
1/2,1,1-1/2, 2, 3, 3-1/2, 4, 4-1/2, 5, 6, 6-1/2,7......



Also, IMHO the 'sound' of a chromatic "dulcimer" is different when you slide from note to note -- because of all the intervening chromatic notes between diatonic notes -- I hear those slides as 'muddier'...

Shhhh!  I have traditionally fretted dulcimers, some with 1.5 6.5 and some that are chromatic. And two with nylon strings.

My favorite dulcimer is the one in my lap.

I think many of the reasons will be be focus on tradition and your music interests which will include style of play [N/D or chording] and need for the extra frets.

It will boil down to what you want plus a bit of DAD [dulcimer acquisition disease].

I am NOT a traditionalist but I find I play mostly traditional [diatonic] music most of the time when I play with others even though my main MDs are chromatic. I use the chromatic side mostly when playing by myself.

I forgot to add, there are 'chromatic tunings' such as DAA#d, but they are 4 equi-distant strings. These are done on the standard diatonic MD.

I am looking to purchase a new dulcimer and am considering getting a chromatic.  It seems the benefits of being able to play any note within the dulcimer's range is a big plus, but I am looking for reasons why I would not want to get a chromatic.  Can anyone provide some insight here?

For instance, does having a chromatic make it more difficult to play classic dulcimer songs, is it generally more confusing, etc...?

Convince me why getting a chromatic is not the way to go, and why a diatonic is better.

Thanks!