I think the answer to that is simple: To make life easier for themselves. And besides, if you expect people to accommodate your handicap, then you should also put an effort in making it easier for people to communicate with you. If not, it's a "Poor me, I'm deaf, YOU deal with it" situation. Not everyone knows how to sign. I actually know a bit, but I can't blame people who don't. Unless you have a family member who is hard of hearing, it actually even makes more sense to learn a foreign language than to learn to sign.
I've always hated the Yield and the U-Turn, since it takes away from actual racing skill. To make it a BLIND U-turn is even worse: You're already an a-hole, and you don't even have to take responsibility for your actions. It probably wouldn't have made a difference today since the team was already in last place, but still, I've always hated this "twist" they added to the game, and now they've made it an easier decision to make for teams that want to use it.
But I actually found it funny that the
deaf-
mute actually got to do the first
blind u-turn, as well.