[imtringued]

>If I just spin up a PostgreSQL database and tell people "hey, I'll store transactions for you – super energy efficient" obviously nobody will use my system.

This happens all the time and there are more of those nobodies than people in the cryptocurrency space.

[fastball]

Can you give me an example? The things that spring to mind for me are generally built on the back of (usually more than one) existing financial system, for example settlement layers at the very least (Visa / Mastercard).