Why North Korea develops missiles for its MiG-29s

Why develop new air-to-air missiles for North Korean MiG-29s instead of spending the money elsewhere?

New missiles can keep an existing fighter fleet useful when replacing the aircraft would be difficult and expensive.

The choice is improving the MiG-29s or finding replacements for them. Developing a missile that works with the existing aircraft keeps those fighters viable when suitable new weapons might otherwise be unavailable. The fleet is estimated at potentially as many as forty Fulcrums, mostly in the 55th Air Regiment. Those aircraft are described as particularly important to Pyongyang's air defence. Better missiles would preserve an existing defensive capability.