(1) If you're buying GME today, there's good (~50%?) chance you'll lose most of your money in two weeks. (Of course there's also a decent chance that you'll make out like a bandit, but I'm not worried about that.)
(2) Moreover, if you're buying GME today, there's a very good chance that you're utterly convinced that you'll make a lot of money.
(3) So, in two weeks, with high probability, these people will flood Robinhood's customer support, and something tells me that they won't take "What do you mean? You made your trade entirely on your own, and nobody can guarantee future prices!" as an answer. (Supporting evidence: see today's talk of lawsuit.)
So, given all this, Robinhood is just limiting the amount of headache it'll face when the shit eventually hits the fan. Sound like good business decision to me.