What leverage do they have? Worker's unions work because they can threaten to withhold labor. Are those students seriously going to not attend MIT? An institution as prestigious as MIT probably has no trouble finding replacements.

When you run a research group: one student leaving is no big deal, every student leaving is a catastrophe. Who's going to fund you when you have no one to do the work? It takes years to get grad students up to speed. All wind is drained from the sails and you need to waste your precious time rebuilding. All because you didn't want to treat your workers like humans.

Withhold work via a strike? See how many labs run and MIT grants are retained without a graduate student labor force.

Except withholding research work also means ceasing degree progress in practice. For some types of work it could mean setting degree progress back months - experiments can be very time sensitive in some fields, and thesis committee will often require certain experiments to graduate.

TAs striking has been somewhat effective, but RAs mostly don't actually strike.

"MIT fires entire graduate student body in union-busting move" is probably not a great look for them.

The would use the term "expells" because they want to say they are students and not employees.

At which point there would be a lawsuit, and they would lose the lawsuit.

Labor labors are an established thing. If a union is approved by the government, then they would have protections.

Same kind of thinking led to empires breaking up.

Failure to accept feedback makes for a fragile institution. Since the students decided to unionize, clearly their issues are not being heard, and a union will have a much stronger public voice than any individual student, perhaps on par with the university's brand and PR campaigns.

Lack of relevancy is no major obstacle to the formation of any sort of political body.