They don't depend on the blockchain, but the fact is that most recent research on these topics has come from the blockchain/cryptocurrency space.

One interpretation is that crypto companies need security and privacy, while big tech doesn't seem to care all that much.

uh... so you're saying hypothetical coinbase cares more about security than hypothetical robinhood or fidelity, or even the good ol' google/apple?

(i'm having a hard time thinking of a successful "crypto" company other than a handful of exchanges, of which coinbase will probably be the only one that survives, at least in the US)

I don’t know if “cares about” is the right phrasing, but financial transactions are a “simple” use case for ZK algorithms. So practicality if implementation definitely affects how much a group or company cares.