Symfony4 - Refresh user roles on every request

I've faced with problem trying to implement simple autorization system in SF4.

class User implements UserInterface {
     // some properties...

     /**
     * @var RoleGroup|null
     * @ORM\ManyToOne(targetEntity="App\Entity\RoleGroup")
     * @ORM\JoinColumn(nullable=true)
     */
     private $roleGroup;

    /** method imposed by built-in UserInterface (SF4) **/
    public function getRoles(): array {
        if(null === $this->roleGroup) return ['ROLE_DEFAULT'];

        /** returns an array of role names **/
        return $this->roleGroup->getRoles();
    }
}

UserProvider:

class UserProvider implements UserProvider 
{   
    public function refreshUser(UserInterface $user)
    {
        $qb = $this->createQueryBuilder('u');
        $qb->select('u, r');
        $qb->leftJoin('u.roleGroup', 'r');
        $qb->where($qb->expr()->eq('u.id', $user->getId()));


        return $qb->getQuery()->getOneOrNullResult();
    }
}

Steps symfony follows:

1. Authentication: after success: The user object is serialized to session (whole, by default), roles are stored separately
2. Refresh user: Security component triggers UserProviderInterface::refreshUser(UserInterface $user) method, coompares them and if objects are not equal it de-authenticates the user (according to documentation)

It's clear and easy to understand, but:

1. Why is the result of an UserInterface::getRoles() separated?
2. Why doesn't SF4 get roles from the serialized User object?
3. Why roles are placed into the session ONCE (after successful authentication)?
4. Why aren't the roles refreshed if an UserProvider refreshes an user every request (by default)?
5. Why doesn't always_authenticate_before_granting => true refresh the user's roles?

Problem: I would like to refresh the user's roles on every request. I am aware I can get rid of the problem via a listener that will refresh token every request, but is there any diffrent solotion?