It’s not just T20 universities where this happens as public flagships have competitive application for activities/clubs etc.
In hindsight – as we were not fans when my kid chose to pledge a fraternity – I understand how greek life can provide a surrogate opportunity for a “buffet” of ECs and engagement in a large university experience. Fraternity and sorority members can get involved leading large fundraisers, from managing advertising and publicity, or they can serve as an officer, managing fairly significant budgets Treasurer etc. While it struck me as “manufactured” at the time – create a group that needs leaders and create fundraisers so someone has to run them – I appreciate that it provided good experience for my kid which helped him get his first job. And, since it is wholly contained within the school experience, a student can navigate the school-EC/engagement balance a little more easily than with a 3rd party non-profit etc. which may have non-negotiable meeting times etc.
But yes, students looking to engage in specific ECs at any school should find out about the process for participating.