Nothing stops tech companies from building crypto wallets or services that hold custody over users funds, a lot of them are already doing that. Building a new blockchain where they fully control the network and its features is harder.
look at atm cards. thaeres like 4 major players globally, controlling everything. I'm not talking about big tech building crypto wallets, I'm talking about them building features similar to what blockchains can do- fake DAOs, fake NFTs etc. the point I'm trying to make is that the end result of all these features doesn't inherently need a blockchain if a major player wants to build them