That’s because she’s typically used as a counter.
I will often start on a different hero, and if the enemy team has a Genji or Tracer, or is running Dive, I will swap to Brigitte ASAP (maybe burn an ult if I have one, then switch) to counter it.
Also, once you get better at pridicting some of the movement from Tracer/Genji/Moira, they get hilariously easy to shut down (at your relative skill level). She can completely counter Rezes, Several Ultimates (Reaper, Reinhardt, etc.).
I don’t have a problem with Brigitte, but the stun probably should not have been added to her. It is the most broken part of her kit, because it can shut down so many things.