Sure there is. Cost per plane, and availability.
A hangar queen cannot meet the needs of the nation, and we can't afford to buy twice the number of planes to account for that because they are so damn expensive to beging with.
Well then I have a bargain for you. A brand new F-4E Phantom cost about $2.5 million. Well it did in the 1960s.
Okay, okay. A new F-15 from Boeing is $100 million, while a new F-22 is $140 million. The F-15 costs $17,465 per hour to fly, and the F-22 costs $19,750 per hour.
As far as I know, the F-22 was on track for an 85% mission capable rate fleetwide last year, and the 525th FS was at 100%. But I guess everyone is hung up on the 62% MC from 2008.