I can't imagine that's a real deterrent is it? Using LESS with Foundation is fairly straightforward. Create an empty .less file and @import 'foundation.css'. Also, LESS and SASS have very similar syntax. There's very little learning curve if you're going from one to the other...

You can't use any of the variables or mixins if you import the CSS in your LESS file. The syntax is not the issue -- the tooling is.

as somebody who uses bootstrap with SASS instead of LESS I can tell you that my reason is simply better community support