That would cause a lot of trains to go over a lot of switches around the DeKalb area, which would slow them down. Plus, that would make it so that all and trains would have to stop at DeKalb, and that would cause some confusion with riders, as it's meant to be fully express. And the only way to get the to stop at DeKalb would be to run it via local north of 36th St. trains running express to make up for the would just mess with the line in general. And there is little to no demand for a west end