You're right! Even though I cited the Sabatier reaction to a coworker today when discussing the news, I didn't really think about it when answering. Also, for some reason I thought it wasn't yet a technical reality.

I guess also wrapped into my statement was the thought that to be able to launch something back it would have to be landed very well and require some very complex machinery to prepare for launch, given the success rates of just being able to land something on Mars without it breaking. I went with the first reason off the top of my head :)