Essentially, the thesis was that a decentralized protocol can never evolve and adapt as quickly as a centralized platform, because the protocol has to reach consensus with all stakeholders before it can change. This leaves a gap between user expectations and the protocol's capabilities, which platforms are happy to fill. They extend the protocol with bespoke and proprietary features, these features draw users, and users come to depend on these extensions. Thus, lock in.
You can see this with email and Gmail, with the web and Facebook et al. NFTs had OpenSea, and crypto in general has the exchanges. You can't separate crypto from the exchanges because the existence of crypto necessarily implies exchanges.