This is probably different. The problem with the subprime crisis was banks had to keep the mortgage assets on their books. They'd buy it -> package it -> sell it. Some banks realized, damn this shit is going to be worthless. And they sold their toxic assets.

Here, the banks don't buy a stake in Uber until they arrange the pool of investors. Or maybe they are selling shares from other clients who want to get out of the investment.

It's doubtful the banks themselves have Uber equity on their books.