The problem is of incompatible time scales. The original studies and requirements for the F-22 were done in the 1980s, Lockheed selected to build the F-22 in the 90s, F-22 entered flight test in 1997, IOC declared in 2005, expected to be in service until the 2040s at least. And in that time the world went from the original IBM PC to iPads and graphics cards that do real time ray-tracing.

And re-doing all the avionics would be a probably decade-plus effort costing billions of dollars. Cheaper to hire some old VAX guys as consultants, pay them exorbitant rates, and have them train up a new generation of VAX people.