Sure, you can do everything yourself but when you use Firebase all that is no longer your concern. It works as if you are interacting with 3rd party API, which means you only care about the request working and you don't care how exactly they are working behind the scenes which means you care about the actual stuff you are building.

Firebase does have some issues but the core premise is solid and IMHO everything will be like that as we go forward.

I am not sure doing this yourself is that problematic. You can get a managed postgres - and that is most of the ops work done. The rest is npm i this/that. The effort is approximately the same as the effort go get to know firebase.

I might be speaking as a jack of all trade so it seems easier to me. For a frontend only dev who needs a backend it might be different.

Of course it’s not that hard but why do it when you can not do it an do something more productive?

My point is firebase felt anything but productive. It had the same mental load as DIY.

I agree in general: I choose netlify/vercel over S3+lambda or vps.