I don't think that we should jump to conclusions just because something takes a while at some point. Do we have any official explanation about this whatsoever? This kind of stuff may have several valid reasons!
It doesn't matter what the "reasons" are. Depositors have a right to withdraw funds whenever the depositor wants to. If Coinbase is legit, it won't hurt them at all if every depositor withdraws all their funds. If Coinbase has been stealing customer funds, it's better to find that out sooner than later.
So withdraw all funds from Coinbase now.