Maybe it is because Some Colleges do not overtly recognize Greek Social Organizations but live with them for Insurance purposes?
Most Greek Organizations will not go to a Campus unless there is a taciturn agreement to the fact!
There is also the fact that none of the Honorary or Professional Organizations have Houses.
There have Been Some Colleges such as Alfred in NY who have de-recognized All Greek Organizations for what a Local did.
There are many who do not recognize Greek Social Organizations but Tolerat them because of the Alum Base that have been Built over The Years and who contribuate to the College Endowment Fund! i think this is true in the Ivy Leauge Schools.
I do not understand, why there is a comparison of Social, Proffesional, and Honoray Greeks about this!
Apples and Oranges! Period! Da!