Why, because so much of this game is mental and with 2 strikes we chase stuff while trying to "defend the plate".
And this comes from coaches and parents acting as if a strike out is the end of the world. Treat a strike out like any other out, and you're developing hitters who will hit more confidently with two strikes. They'll be less likely to chase or "expand their zone" beyond what they're capable of hitting. They'll strike out a little more, but they're also going to make a lot better contact with two strikes.
This will serve them well when they advance past the level where "just put the ball in play" means a team full of bad defenders throws the ball around and you reach on a series of errors.