Either no one told them or if they were told, they ignored what was told to them and continued doing what they were doing. or they have no one to teach them the Taeguek poomsae so they keep doing what they are doing.
Here, only one dojang continues to do the Palgwae poomsae, which they adopted a couple few years ago as a compromise (in their mind). They went from Chang Hon forms to Palgwae because they felt going straight to the Taeguek poomsae was somehow too radical a change. They also are the only school that still wears cross over uniforms, and they consider themselves to be "traditional" Taekwondo. The instructor I believe has a dojang 3rd Dan and uses Japanese terminology in class. But they bring a lot of students to the local tournaments so they are/have been tolerated. But at some point in the very near future, the Palgwae poomsae will no longer be accepted, and we may lose their participation at our local events. There are other Taekwondo schools, but they don't participate at our tournaments and stay to themselves.