OpenSea does have some advantages of network effects and has been able to mostly fend off LooksRare, despite charging a 2.5% vs LR's 2% marketplace fee. There's no way they could have done so if they charged 25% and users could save 23% on every transaction by moving to LooksRare. Similarly, if Airbnb were "open database" and anybody on the internet could build a competitor that used the same data set, there's no way they could take the high fees they currently do. They don't have to, since they're web2, though. All the data about hosts, guests and ratings is in their database and they don't have to share it with incumbents.
Social media companies would feel this, too. A huge part of their lock-in is that they own the social graph. It would be a very different situation if that data were on-chain and anyone who wanted to could write a different front-end to surface the same data (some cloning the look and feel closely and other choosing to surface different subsets of the data in different ways).