My D is at WashU and she isn’t part of Greek life and you don’t have to be if you don’t want to. There’s no pressure. She does attend some formals or parties.
About 35% are part of Greek life at WashU.
However at Dartmouth, over 64% are part of Greek life. That’s a big difference.
http://www.dartmouth.edu/stulife/greek-soc/glos_chapter_size_winter_16.pdf