It almost feels like you'd want to do the opposite, given keycloak is a traditional community open source project while zitadel is a startup=project of the type that has been closing up their licensing en masse in the last few years.

Keycloak isn't very nice to work with in short. It's still not very cloud native and is just a big chunk of software that implements god and the world even if you don't need it to. It's weird to customize as well (thinking of theming and the SPIs).