From browsing r/ErgoMechKeyboards and GeekHack, I think the main group of people making these custom keyboards are devs actually. Consider how foot pedals are a long-standing emacs thing :)
I use a 40% layout on a custom board with palm keys for coding and writing in LaTeX mainly (like the Model 01 with 3x6 alphas 3 thumbs 1 palm on each side). It took some effort to re-train, but I'll never go back to a keyboard without palm keys now, I love the setup. They palm keys are perfect for activating the layers for arrows/navigation or numpad. But typing style plays a role too, it's definitely probably not everyone!
I code full time on an Iris. Hold/tap is huge for me for every kind of bracket or brace, just like the spacecadet keyboard that came before us. I have my layer modifiers under F, D, and S which then flip the right hand to Vim style arrows, a number pad, and a symbol pad.
I use my Ergodox full-time and I love it, but I feel this way about an Atreus I just picked up: there are only a few keys, and some are inaccessible (!) so I'm stuck putting stuff like colons and quotation marks in a layer. Feels bad.
Agreed! I tried all kinds of keyboards, and intensely dislike all these smaller ones, which I find absolutely unusable for anything more complex than typing email.
Some people quite visibly disagree with me
I eventually settled on a kinesis ergo edge, which I really like.
I have a keyboardio model 01(this: https://shop.keyboard.io/collections/model-01-keycaps/produc...)
And even this feels like I'm having to function dive into weird chords of keys to get some of the functionality that I want (arrow keys, mostly).
Are people just not actually writing code with these ultra minimalist things?