gpa

The key word is recommended. A 3.0 is recommended as the "starting point" to be considered by sororities, but obviously every sorority wants to see something higher than that. Some sororities put a heavier emphasis on grades than others, which is why you may feel there's a discrepancy between what Panhellenic says and what the individual sororities say. Overall, each sorority has a standard GPA that they want PNMs to meet and you can find those standard GPAs in the Greek Chic booklet. Panhellenic suggests a 3.0 as an average of standard GPA requirements for all the houses.
But honestly, sororities take so many different things into consideration. Some houses are more lenient towards grades if you meet some of their other requirements. Overall a 3.0 is a fine GPA for a handful of houses here.

3.0 is the hard cutoff for many (if not all) sororities, but we would prefer you be much higher than that. For example, at my house, from 3.0-3.3 is seen as a negative (and anything sub 3.0 is a HELL NO except for the most extreme circumstances - like 2 or 3 girls a year). However, you can counteract those negatives with positives, like connections, looks, etc.

If you have a 3.0 though, you still have a very good chance of getting a house, you just won't have many options to choose from. Weaker recruiting chapters don't get to cut as many girls, and they have more parties than stronger chapters, so all the 3.0 girls will be attending the same parties.