Hi, I can completely understand the frustration and you have every right to feel that way. That being said, as a modder, here's my perspective on why it happens:
1) Statistically, the fandom prefers normie bodytype 1/2 characters, so it's just more likely that mods will be made for those characters. To most people who do it, modding is a very personal endeavor and most of the mods are made based on the author's personal tastes, and a big chunk of the fandom prefers elven/tiefling/human BT1/BT2 characters.
2) Modding heads and armors can be a long and tedious process. To put it in context, every equipable armor you see in-game has 14-16 different meshes, for each race and bodytype. This might seem easy when done with Larian, a company with resources and trained professionals, but when you as a modder have to refit something sixteen different times by yourself, by hand, it gets tiring real soon. Add to that a bunch of issues with clipping and physics that are often hard to fix, and you have a very tedious, frustrating, and long process with no significant financial compensation most of the time, unless it's a commission. That's why a lot of the armor mods are often limited to a certain bodytype and race.
I get that it's frustrating, but please keep in mind that armor making in particular sucks for everyone.