Seriously you'd think on a board ostensibly obsessed with CAC and ARPU metrics, it would be immediately obvious why a specialty player wouldn't want to compete with Schwab and Fidelity.
Multiple players along the chain could decide to vertically integrate. Although I used the example of high frequency traders, a better question which I should have asked is why hasn't someone dipped their toes into retail and HFT? It seems like someone would want to grab that land for themselves if it were particularly valuable, which the valuation of Robinhood purports. Considering some guys in that industry made this app, I don't think it's too far a stretch of the imagination for someone to believe that an industry player could have made that move.
If you're an HFT, you would much rather just pay for the order flow and not deal with all the shit that is retail (government, customers, all that shit). If you're some big retail firm, you're probably run by suits, way to beauracratic to run a difficult high-tech trading team, and any talent you got would get siphoned off to a good trading firm.
different competencies. Acquiring retail customers is very hard and is not something HFT firms have any special competency in.