The problem is students are not very hardy activists. They are enthusiastic, sure, but American students have to pay to be there and operate on strict schedules. Many of these student orgs conceded because summer break was going to destroy their organizational manpower no matter what they did. Additionally the universities hold lots of power over students: access to food, housing, even visas can be revoked. Students are fighting on enemy territory and holding a occupation of a student union building causes far less economic damage than a labor strike. Then theres the socioeconomic aspect where most of these protesting students are either poor, struggling and indebted or middle class first rally ever types who can't handle institutional or police pressure. Not blaming them, everyone starts somewhere, but there are serious limits to student activism, at least in America.
Edit: felt like i was being too pessimistic so want to add that students working in conjunction with other sectors of society can be a really potent force. For example university staff or labor unions joining with students. When student enthusiasm can be supplied with wider resources and organization the authorities start getting really scared. That happened a few times and we saw how it came with massive crackdowns but even then the students at UCLA and Columbia put up a good fight against a goddamn freikorps and psycho NY cops. A lot of other places were able to resist police and administrative attack, so although divestment largely wasn't successful perhaps thousands of radical students have learned some important lessons not taught in class.
I think of the May Fourth Movement in China, and how many future leaders of the CPC were shaped by those largely student driven protests. Our future has not yet been written.