DoorDash purchased Caviar from Square last August: https://techcrunch.com/2019/08/01/doordash-is-buying-caviar-...
I assume DoorDash doesn't want to alienate loyal Caviar customers and so is continuing to operate it independently, similar to how Grubhub and Seamless merged seven years ago but still run two different websites (albeit with identical design).
Maybe have them try the arbitrage themselves per the article and put the profit _and_ the booze directly in their pockets... (/s?)