You are correct that injuries happen, and that they can happen to anyone.
The fact is, however, irrespective of the reasons, some players are more injury prone than others.
The fact that Tua's ankle surgeries were "elective", doesn't make me feel any better whatsoever.
An NFL playoff run is almost twice as many games as a collegiate season. The guys are bigger, faster, and he will take a lot more hits.
He may turn out to be a good QB, but I doubt you ever get a full, healthy season out of the guy.