Highly likely that it is at least partially because Boulder has more distractions – students do a lot of skiing, and a party CAN be found any time by a student who is looking for one (not saying that a serious student can’t do well, though – my brother had a business degree from CU and graduated in 4 years).
In addition to my nephew at CSU"s observations, we used to go to summer band camp at MSU every summer. Sometimes we would walk to various places on campus when we had a few free hours. I remember hustling to make it back on foot in an hour from some locations to the dorms where we stayed and practiced.