Just brainstorming here.

You suggest that an anonymous mint could be trusted if it had more bitcoins locked up in a smart contract than in the wallet for its users provided that the users had a way to grab those bitcoins if their funds don't get honored.

This requires a lot: Knowledge of outstanding IOUs. Knowledge of funds under reserve. The bond being distributed between many users that often might not have significant balances individually, justifying an on-chain transaction. After all that's why many use a mint.

In order to prevent rug-pulls, it does not matter where the funds flow as long as they don't flow to the hacker. By paying out to users, you almost can't prevent the hacker from holding an insane amount of IOUs, diluting all other user's claims. Therefore it's more feasible to just send the bond to a burner address.