Why is Bluebonnet so bad?

Every day I take my girlfriend to and from work going down Bluebonnet onto Airline to get to her job. Every day coming back I hit insane traffic where Bluebonnet intersects with Jefferson Highway. Why are so many people turning onto Jefferson and downright blocking Bluebonnet, leading to this massive jam. It's really only this stretch of it, it's awful. I took Siegen the other morning and was shocked by how *empty* it was. I won't be taking Bluebonnet in the mornings or going toward her job in the evenings anymore because people don't know how to act on this road. I just want some clarity as to why the logjam of traffic occurs every single morning, is it people who don't know alternate routes exist? Is it just stubborn people who have been taking this trek every morning for the past 20+ years?