Every extra they tack on to the base product is one they will be expected to deliver on as well diverting attention from the main problem they are dealing with, which may in the longer term leave open enough room for the competition to wiggle through.
Sure, autonomy is a big deal, but it is also something that will once cracked be an instant commodity and there is a lot of money and talent focused on that particular problem, which is surprisingly hard to do well.
If Tesla ends up going under because of one of the side shows (Solar City, autonomy, Power Wall etc) that would be a serious loss.