why do both

I know people will hate what I have to say here, but they're completely different. The people who are only in spirit groups will tell you they're just like a sorority, but they aren't. They're all people who couldn't get into one of the good sororities or couldn't afford a sorority.

The people who are in both are those kind of people who are active and joiners. It's a good option to fulfill any sorority campus involvement requirements and sometimes it has to do with family tradition.

There is also a definite tier structure in the spirit groups. All spirit groups are not created equal.