Simply put, Robinhood has far more at risk than the SIPC by launching without SIPC insurance. The banking industry is heavily regulated and Robinhood has been in the brokerage game for enough now to know that a major product launch like this in a tightly regulated area requires massive amounts of paperwork and approval. A mistake like this could collapse not only this new product but also their brokerage. It's far more likely that they have done their due diligence before announcing and launching a product that has that big of a risk.