For most of the accounts- it wasn't a significant amount at the time they deposited. Indeed many wallets were probably abandoned.
Exactly. 50 BTC at Christmas time was $500. Might be convenient for some to have it easily spendable from a web wallet. Now, it's $5,000 or so, and a different story.
Think about the people that used it back when bitcoin was worth a couple of bucks and abandoned 10 BTC. There may be plenty of coins available for those that want to claim them plus plenty of profit for shutting her down.