>>22883
Because any mesh body worth anything has several layers to apply texture clothing on. These are stacked on top of each other which would make manually selecting them a pain in the ass.
On top of that those mesh bodies also are segmented so you can hide parts of them, making manually selecting even harder (you can't just apply 1 texture to the whole object because the SL uv map has 3 uv spaces).
Making them mod would be nice, but from a creator's perspective would be more bothersome than it's worth, since idiots would fuck it up and then come crying to them.
Not everything is as simple as some furry fetish body with no clothes.