https://en.wikipedia.org/wiki/National_best_bid_and_offer

They don't need to frontrun they'll clean up just from providing liquidity with the huge volatility in the symbol.

Citadel is split into Citadel Securities (the market making org which pays for orderflow) and the Citadel the hedge fund. The two halves of the business can't coordinate/share position info (or order flow info like others have implied). If they did they'd get absolutely demolished by the SEC. There is really no reason for them to do that though since they're already printing money from MMing.