>>64135710 (OP)
Planes were highly specialized until fairly recently. Interceptors, fighters, night fighters, tactical bombers, strategic bombers, reconnaissance... Not to even mention all the support roles.
Hell, most of those categorizations still exist. It's just the lighter airframes which have become modular thanks to advances in propulsion allowing them to carry a wide array of standardized gear. Why build several different kinds of planes, when one can do the job with specialized loadout? They've got the carrying capacity.
You can't pull out the most of the armor and the turret off an MBT and make it into a self-propelled howitzer in fifteen minutes. But pluck out the AAM's and tack on guided bombs, and presto. A truck into a recon vehicle? Won't do. Stick on additional sensors and/or an electronic warfare suite? You got it.