I have no idea what your point is. People write in Java, Ruby, Lisp, Javascript, and any of 50 other languages to avoid writing bare-metal C, too.
We recently had to fire a design team and are in the process of moving to a different team. If all the styles were in SASS, I'd have a much bigger problem.
Even something like LessCSS has a much smaller learning curve because it looks like CSS. You can use it much more minimally (using only variables, for example) and get a small benefit with a small learning curve. Think of how many of those 50 other languages look like C.
If your designers can't grok Sass, you do what every professional team using template languages has always done; you back-and-forth with the designer in CSS/HTML, and you convert final comps to templates. Designers by and large don't speak Haml, Erb, Clearsilver, or Cheetarah (or Mum-raah or whatever Django calls it) either.
Templates are a different story -- that's where the design and the functionality meet. I do convert the final comps to templates and if necessary the templates back into static code to repeat the process (rarely necessary, but it happens). This is a necessary evil. Why would I want to perpetuate that evil in CSS as well?
If they had given you their Sass code, you would be empowered to make design changes much more easily that you could have with CSS. If I were you, I'd be demanding that my designers use it ;-)