Your employer is an entity (a person, an LLC, or a corporation), you work for that entity. The entity is allowed to distribute it among themselves but the entity prevents itself from distributing to others (by following the license constraints). You, the employee, do not gain the right to the software because the employer did not give you, personally, any permission to the software.

Only once the software has been distributed by the employer to a third party do you, the employee, get rights to that GPL software. You can replace GPL with other licenses, the premise remains the same: an employee is part of the employer and not a separate entity.