I'm not sure I understand what you mean by locking sats for orders, but I don't think it matters. The problem is you can prove that your list of deposits / orders is complete and you didn't delete a entry.

Let's use a simplified example: Let's say you and I both have 1 BTC deposited on Kraken. Kraken in turn publishes a list of deposits stating they owe account A and account B 1 BTC each, and they have a list of addresses that have 3 BTC. Then it looks like they are 130% reserved, because they need to provide up to 2 BTC on request but have 3.

However Kraken actually has one more account C that is owed 2 BTC - Meaning they're actually 3 / 5 = 60% reserved, not 130%. Now if everyone takes out their BTC at once the last person will be rugged.

 The problem is basically you can prove how much Bitcoin you have, but not how much Bitcoin you owe. Because you'd have to prove a negative, I.E "prove you don't have more deposits than you published".