>>63810832Long-range missiles are are heavier and wider diameter, the drag increase proportionally worsens the range increase, and increasing the weight makes it more difficult for ground crew to handle. An AMRAAM can be installed with no equipment, a 1000 lb R-37 needs a powered loader.
And as for actual range increase, there's diminishing returns as well. The longer the time to intercept is, the more time the target has to turn away and waste the missile shot.
Guidance also used to be a bigger problem, datalink cueing is a somewhat new feature, datalink cue from 3rd party radar is an even newer feature. Back then it didn't make sense to design a missile that can be shot further out than the radar can see. Odds of the datalink being jammed also increase the further you shoot, but EW is a dumb topic on 4chan.
tldr more expensive and worse aerodynamics, bit of the same reason why infantry uses 5.56 instead of 7.62 NATO (nevermind the M7)