Description
So, the EntityRepository class has all the properties marked as private readonly. The expectation here is that you're going to construct your repository class with these and they'd never need to be changed.
Then comes the repository factory, which returns the repository for use with the EntityManager.
It seems the decision has been made that your repository classes should only be accessed through the EntityManager and that the constructor of your repositories shouldn't be available to pass additional services.
If you attempt to instantiate your repositories with additional services (different per service as would be the logical case), say with a service container - that'll work fine, but you must then use that container within the factory to return your instantiated repositories.
The issue here is that you're now stuck with an EntityManager that's pre-defined for that repository. You cannot pass or update the EntityManager associated with a repository through the factory. If you're using a custom EntityManager, say with a specific connection, and you call $em->getRepository(Foo::class), you'll then end up with the pre-defined EntityManager on that repository, not the EntityManager you're currently calling getRepository with. And, because everything is private readonly on the EntityRepository, you cannot update it either.
Also, the RepositoryFactory::getRepository method is typed to return the EntityRepository and not an interface. So you have to extend the EntityRepository. Otherwise, you could just wrap it and compose your own base class.