Due to the actions of Fantastic Four villain Dr. Doom (who manipulated the deaths of the Scarlet Witch, and the conflict between the Brotherhood of Mutants and the Ultimates), Magneto vengefully executed his plan in exterminating humanity through shifting the poles of the Earth, causing global natural disasters upon the world, leaving only he and his followers to survive. In the wake of Magneto's fury, millions of people died including many of Earth's superhuman heroes and villains alike. Anti-Mutant sentiment was exacerbated in America and with the majority of their members dead, the X-Men disbanded after their leader Cyclops was killed in an assassination orchestrated by the Brotherhood, now lead by Magneto's son Quicksilver. Mutants began to be arrested and shipped off to internment camps.
We might want to consider what we’re fighting against first. As has been proved countless times artillery is the main killer on the battlefield. Artillery shell produces fragments against which we can use rather light weight flak vests. Now were reasonably protected against 80% of the possible threats. Then there’s tanks and apcs, no way we can be armored against 120mm tank shell or 30mm cannon shell but we can be protected against their fragments. Fighting Jihadi Johns in rags wielding Pa’s AK has warped our view about what is reasonable level of protection. It’s fine to be overburdened if you have the luxury of waiting 15 minutes for airforce to bomb JJ into the Stone age but that won’t be the case against competent enemy.