Because it isn't a simple loan, and the value of the equipment itself as collateral is highly doubtful anyways.

Nvidia is investing in their customers by buying their stock. Nvidia is directly buying compute from their customers. Nvidia is making "if you can't find a customer, we'll take all of your capacity" deals. Nvidia is making a ton of fake huge-number deals which are supposed to be realized over time but most likely never will.

They are doing everything they can to make that customer look like a healthy and valuable business which everyone should invest in and loan money to - which in turn flows directly back to Nvidia to buy GPUs and boost their revenue. They are essentially creating sockpuppets to keep external money flowing in so they can keep the money printer running.