Have you ever noticed when you go to use the bathroom your dog follows you in there and just kind of wants to hang out? Even if you shut the door, they're right there or they try to open the door.
You have have heard before that Dogs view you as a member of their pack and when wolves and wild dogs use the pack protects them because going to the bathroom makes them vulnerable. So your dog is following you for extra protection.
But that's not the only reason. They also could be curious or just enjoy your company. Ultimately, they just adore you and want to be with you.
We don't deserve dogs.
Source: YourTango