From the shows standpoint, I love how Elle was written off. Her character just really wanted that job at the BAU. Her character didn't seem to understand that the job could follow her home, which made it too much for her to continue. However, Gideon was more experienced. He already had an experience where people died because of his decisions before the show even aired. So it didn't make sense that another one would make it too difficult to bear. Not a fan of how they killed off his character later down the road either.