For the same reason some time ago I asked about to use Coffeescript and people didn't approve in favor of Babel, Less should be dropped in favor of PostCSS:
I't use standards, and with the right plugins you can write the next CSS standard right now.
Take a look at this post: http://davidtheclark.com/excited-about-postcss/
I don't think we should re-write all stuff right now, but we should think about it sometime