The ground isn’t honestly all that dirty, and in many cases players are butchering animals on concrete, asphalt, wood floors, etc. The real problem when you’re butchering is that if you nick the guts you can spoil the meat by exposing it to bacteria that was in the animal’s digestive system. This is where e.coli comes from a lot of the time. That kind of thing could be a survival check that a surface would give you a bonus to, I’d buy that much more than my character not knowing how to get a thigh from a dead bird without there being a plastic sheet on the floor.
This article talks about it a bit. I assume that’s also part of the intended difference between quick and full butchery though - you can’t safely get as much meat if you can’t get it out of the carcass without contaminating it. Again it really just seems like the surface is an unnecessary step that was already accounted for, and maybe what was really wanted here was to make butchering less risk-free.