A local paper covers the new “professional adversaries” for Langley Air Force based F-22 Raptors.

[Lt. Col. Derek] Wyler and several other pilots at Langley Air Force Base fly the T-38 Talon. First used in the 1960s as a trainer, the Talon has been given new life at Langley and two other Air Force bases. It plays the role of enemy aircraft in training exercises with the F-22 Raptor, now the top-line fighter in the fleet.

While there are some challenging characteristics of the T-38s which make them desirable adversaries, it probably comes down to money: it’s just cheaper.