why do some not have houses?

A lack of brownstones on Columbia’s part. Columbia also doesn’t particularly love Greeklife, so it prioritizes brownstones for special interest communities over Greek organizations.

The sororitys that don't are also the newest chapters on campus. It makes sense why they don't have a brownstone yet. I would reach out to members in those sororities to find out more about this.

The 2 sororities are the “newer” sororities and therefore do not have brownstones. They probably won’t get brownstones until both have the opportunity so that there is a level recruitment field. Just because they don’t have a house doesn’t mean they don’t have spaces to hang out and even if you do have a house there’s no guarantee that you hang out there all the time, especially if your closest sisters don’t. A house is a great fall back zone but it doesn’t make the sorority. Girls I know in the 2 chapters w/o a house usually end up getting large EC, 600s, Ruggles, Plimpton, or Sulz tower suites together and everyone just hangs out there. Sisters are pretty receptive to making use of their own spaces to subsidize for the lack of a brownstone. Good luck in recruitment!