It's the same reason there isn't a central email sign on. Different people control different servers. They're all just using the same protocol so they are interoperable. Just like your email, you have an address that points to your particular account on your particular provider. Name@host.tld. It's essentially the same thing as email, just a different form of interaction.
oauth does exist, I think some fedi platforms do support it even.
Oversimplification ahead.
Oauth is a solution when single provider offers many services.
Lemmy is a single service offered by many providers.
While you can work around some of that, that is still the essence of the "problem".
It's the same reason there isn't a central email sign on. Different people control different servers. They're all just using the same protocol so they are interoperable. Just like your email, you have an address that points to your particular account on your particular provider. Name@host.tld. It's essentially the same thing as email, just a different form of interaction.
oauth does exist, I think some fedi platforms do support it even.
Oversimplification ahead.
Oauth is a solution when single provider offers many services.
Lemmy is a single service offered by many providers.
While you can work around some of that, that is still the essence of the "problem".
That was an excellent EIL5