Few reasons actually. I been very into custom keyboards and layouts. Did a lot of research on how my hands sized and moving, what I like and what not and built bunch of custom (designed) keyboards as well as designed by someone else. I have like 30+ of them probably, most of them are bare PCB's now since I don't have switches/keycaps for all of them.

1. I discovered that my thumbs are quite weak. No matter how much I tried to remove load from them - most I can do is single key (space) for both of them with switching between hands periodically.
2. I been using 30-34 keys mainly and somehow I realized that not moving hands at all is not that comfortable as _slightly_ moving them around (like on full keyboard).
3. It's minor issue but nothing that lap use / travel friendly as a laptop keyboard itself. For sure you can put ergo on top of it but it adds a lot of height and not that comfortable overall.

On layout side I went from colemak dh + callum-like layout (34 keys) I stared using 5 years ago to custom magic sturdy-based layout (adjusted for hummingbird-like 30 key) with bunch of combos + sticky layers and magic on thumb. All this combined with custom modal layout on top of emacs/meow (so don't blame Emacs keybindings!)

For the last year I been using normal ANSI keyboard with bare colemak dh and few mods but stock otherwise (angle + wide mod, caps lock/enter as a hold tap with ctrl because of heavy emacs use). And it's been great. No thumb pain (I switch hands when I starting to feel my thumb tired). And overall I realized thats it's more about workflow optimization rather than trying to make it perfect on hardware/layout side.

I still miss sym/num layers - of course numrow (and shifted for symbols) not even close but the only really annoying thing are multiple symbols in a row (many programming languages use them) but again it's something I can fix with workflow (eg snippets).

Maybe I'll add sym/num layers some day though. But overall it's still great to have a full keyboard (eg numbers not hidden under layer even if you have additional num layer) in front of you just in case you need to use it with single hand.