It's more likely they realize trying to collect on that money would kick off a protracted legal battle, which they might lose. Investors do have some protection

It's more likely they realize trying to collect on that money would kick off a protracted legal battle, which they might lose. Investors do have some protections, and a glitch allowing infinite leverage is a definite, absolute fuck-up on Robinhood's part, which might be exploitable in court, not to mention the bad publicity it'd bring. (E.g. Robinhood sues working family into bankruptcy over glitch in its own app.)