Depending on the university or college you attend, there will be a (small) group of political organisations who traditionally dominate local student politics, and have the infrastructure (and possibly the cash) to prevent independents and candidates from other political groups from winning elections.
My 1st university (in the West of Scotland) was dominated by one political group (Labour Students - the West of Scotland elects anything with a Labour rosette). "Independent candidates" were non-Labour Students who just happened to have a Labour Party membership card (or, at best, were "fellow travellers").
Look at a National Union of Students conference, and see just how many independents there are - the vast majority of delegates are members of one or other political group.
This isn't intended to be a complaint against Labour/Labour Students: they were simply the dominant group at my university. Other groups that dominate on campus include various Trotskyist organisations that are immensely powerful on their own campuses, but virtually unheard of in real-world politics, and the Union of Jewish Students, who are huge in London and the South East but - naturally - don't exist outside of student politics.