A reflection of the hole that the USAF/ANG is in with the cost of replacement aircraft.
The average age of the F-16 fleet is now 30 years. The average age of the F-15C fleet is now 38 years.
The replacement F-15EX buy has cut and capped at 80, now earmarked to carry the new HACM (echoing the M31 and Kinzhal) with the Sec of State for the AF informing Congress in April that, as airframe life runs, the remains F-15C units will either be replaced by unmanned aircraft - or not at all.