How do colleges know if you're doing multiple degrees at the same time ?

[alzee]

Right, if you ran a private college you can do whatever you want. But if you are running a taxpayer supported college, you have to think about spreading the resource out to benefit as many people as possible. Most of the cost of educating a student is borne by the taxpayers, not the students. Every student pursuing a second, third, or fourth bachelor's degree is taking a spot away from a first time college student.

Using "the taxpayers" is a bit over the top -- it's not as though they're being consulted for their opinion on the matter, and as is obvious here, not all taxpayers are on the same page.