The rationale is that the CDC measures have proven ineffective and they've shown to not have health as their priority, to say the least. The shift to 5 days quarantine came a few days after an urge from the Delta CEO, I believe. Fauci's own justification did not involve much health, it was all about the economy. The CDC was also ignored by the very same people saying that we should listen to the CDC now, just like vice versa. Yet, you can look at the data and see that the US had 1mm cases in a single day and ICUs are starting to get overwhelmed again. Not days after the CDC's measures.
And yes, the colleges might be doing this to cover their ass, but if the end result is lessening the spread of a brand new disease that has already killed a lot and severely damaged many others, I'm OK with that.
TLDR: people are still brushing off the death of a large number of young adults because they don't want to be inconvenienced. Now might even be too late, but I'm personally not a fan of "ay man, we tried, let's just run it and see how it goes" when it comes to this.