Sorry for the late response. This question would be best suited for the Graduate Student Government (GSG). From joint meetings last year, I believe GSG said it was because online grad students pay $999 a credit hour and they do not pay fees. Many of the on campus resources are only available through these fees. This is certainly something to bring up to GSG as I imagine many other students are in your situation. The president is Maxwell Silver and his email is gsgpresident@mines.edu
-USG