Remember the Atlantic 10 would have not been able to invite schoolsfrom FCS until it had 8 full members playing FBS football itself. At the best case, the A-10 would have needed the following to go FBS:

UMass moving football from the MAC in 2013 (first season out of transition)
Temple staying (George Mason stays in CAA)
Cincinnati replacing Xavier (Xavier to Big East)
UConn joining as a full member (VCU not added in 2012)
South Florida added as a full member (Butler to Big East)
Memphis added as a full member
Central Florida added as a full member
Georgia State added as a full member in 2013 (first season out of transition)
Charlotte staying (Davidson not added in 2014), bowl eligible in 2015; first FCS invite

That's a net add of four members just to get to nine in football. That would push conference membership to 19 assuming the Big East stopped at 10 members. Even if the Big East took Saint Louis and either Dayton or Richmond, 17 is still too many members for a conference. Of course if this had happened, the CAA now has Davidson, VCU, and George Mason.