The suits aren’t technically needed for reentry, since the capsule isn’t supposed to be depressurized at any point during the trip. It’s just another layer of “if something goes wrong.” So if it’s a choice of taking that risk or staying on an exploding ISS you go with the risk. I expect that even if the suit can’t be connected to Dragon’s umbilicals it could still be sealed for at least a few minutes of air during the riskiest bits of the trip.

As with most safety procedures, it’s written in blood.