dakareng is correct, the reason there aren't more chapters at IU has everything to do with housing or lack thereof. I think the IU PHC has a rule that a chapter can only expand if they will be able to build a house within a certain amount of time. (Maybe someone who was actually in a house at IU can verify this!) There doesn't seem to be any such rule that applies to fraternities, so that explains why several have colonized or recolonized in the last five or so years, while the only successful recolonization of a sorority in that time was AOPi, and they bought the old KDRho property and built their new house there. All the houses are ginormous and it probably takes quite a bit of money to keep them up. Thus, every sorority at IU has a residency requirement of 2-3 years, depending on the chapter...at least they did when I rushed. (It's not a question of if you want to live in the house, you're going to live there...and all PNMs know this going through.)
When I rushed in the early 90s, four sororities were housed in one of the dorms: ADPi, AXiD, ASA, and Tri-Sigma. The first two had land and were able to build houses in that time...therefore they're still around. The second two did not and I think that was a big part of the reason they folded. After all, the point of going Greek for many people was to get out of a dorm, not to stay in.

Several fraternities have been closed down by the university since then but I think their nationals still own the houses. The old AOPi house was sold to IU, as were some other former Greek houses, and the old Sigma Kappa house was sold to Pi Kappa Phi.