You aren’t thinking this through. If a startup defaults, it is because they have no money left (which is because they do not have a viable business yet). So there is nothing of value to repossess.
This is the same reason the bank asks for an independent valuation of a house (and requires the buyer to maintain insurance) before releasing the money to pay for it: The value of the collateral needs to plausibly match the value of the loan, so that the value of the loan can be recovered in case of default.
The only way this works is for the founder to personally guarantee the loan. Which means the founder needs to have sufficient personal assets to keep the bank happy. It also means the founder risks personal bankruptcy if those assets are not enough to cover the loan if the startup defaults.