But GrapheneOS doesn't exist. It works only on a few devices created by Google, so their claim of being degoogled is a bit funny.

Not everything have to be perfect.

For some user, /e/ is more approachable (Friendly and colorful UI)

I could not get my mother to use GrapheneOS, /e/ is a lot simpler.

Still miles better than to use a Default ROM from most OEM.

Even on non-pixel devices, unless you really want to use the /e/ "ecosystem, there are probably better options like LineageOS for microG iodéOS.

(/e/ used to be heavily based on an outdated version of LineageOS for microG. I'm not sure what the current state is after I settled on second-hand pixel with graphene)

Unless you own some obscure phone that is not supported by GOS, Calyx or Iode, but is by /e/... Not sure how many of those exist...

There is when you have a phone that isn't a pixel.

And even if GOS doesn't support your device (due to minimum security requirements) why not use upstream LineageOS?