You know a whole the size of a quarter can wreck the entire spacecraft and make it effectively throw away? Also, you'd want to use this many times. Making a system robust while not requiring months of refurbishment is really really hard.
coming back in one piece, and being good enough to use for 5 more missions are two very different things. For example, all existing reentry vehicles come back "fine" but they need to be completely remade to go up again.
Deliberately testing its survivability with that failure mode over different parts of the vehicle has been one of the major foci throughout the entire test campaign, and it has proven remarkably resilient. That generalisation pretty much does not hold for starship.
