They did but back then it was still a bit unclear who was going to emerge as the de-facto standard. They made the wrong choice, and now they're correcting it. Good on them for not sticking to their guns.
Sorry, my comment was probably a bit flippant, and I meant no disrespect to LESS as a technology or a choice. There's nothing wrong with LESS..
That said, the major CSS frameworks that I am familiar with (Foundation, Bootstrap, Bourbon, etc) all seem to be choosing SASS, so it feels like it is becoming the de-facto standard..
I'm sure there are lots of excellent and well-supported products that still use LESS though.