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

[TrailRunr]

This doesn't make sense. It does not cost them any more to grant a degree than to deny it, unless the graduation fee is significantly less than the actual cost of graduation, which I find impossible to believe. It's probably some misguided attempt at equal opportunity, as in they likely don't want people seeking their 2nd, 3rd or 23rd degree filling classes and making it impossible for those seeking their 1st to enroll.

The University of California has academic residency requirements that is effectively 24 credits and two terms after you become a senior. You can't transfer the credits from outside. Like you said, they don't want to take a seat away from someone with no degrees. Furthermore, there is the issue of the taxpayer subsidizing additional degrees.