GrapheneOS is significantly more secure, more private, and more free. Not sure why you would use /e/.
Because in order to use Graphene, you have to financially support the same company that is making Android less free.
Well, for one you can actually buy an /e/ device right now.
Also, once you have it, it just works.
Some people like that.
and limited to one type of device that not everyone can get or wants.