If you think you're being clever, you really need to read up on the legacy of the GI Bill. Perhaps, you could start by reading the article I linked to.
If it's going to college that fuels social mobility, then more people going to college today than in 1940s and 50s should mean more social mobility today. Since allegedly the opposite is true, there must have been something else different between 1940s and 50s and now, that has nothing to do with GI Bill funding more people going to college.
If you think you're being clever
There's no need for snark.
you really need to read up on the legacy of the GI Bill. Perhaps, you could start by reading the article I linked to
If you have a point, please make it explicitly, instead of having me guess it.
Straight entrance numbers are not the best comparison.