The US military has thousands of old airframes, many of which can be made flyable with very short turnaround. They already use the F-16 as test targets.

Taking an obsolete airframe that is already paid for and adding AI to it is much cheaper than building a completely new AI-native airframe from scratch. This is finding a new use for old aircraft. You can send a bunch of old AI-driven F-16s on high-risk missions without worrying about a human pilot or cost. The airframes may be relatively obsolete but can still do plenty of damage on their day.

The new 6th generation aircraft are all being designed as "manned optional". That is probably the last generation with affordances for a pilot.