I spoke with one importer re. that specific topic. He wanted to know what was involved (time, effort, resources) to downgrade things before they left his hands because he was quite concerned about some new uninitiate buying one and hurting someone at a game.
It would have been massively more simple for him to simply receive and sell the items. Instead he opted to buy additional springs and pay for local labour to swap out, function test and chrony each item. PITA to be sure.
Anyways...that was a thankless endeavor. Those that wanted a sub 400 FPS didn't think anything of it....and everyone else just shat on him for his "audacity" to "compromise" a factory gun.
So....many retailers don't bother. And here are the results....
Pointed example...some idiot bought a new rifle for a sub350 indoor game. Just got it. Shot the first couple of games with it before someone made the host chrony. Bang, bang....his fresh out the box rifle was shooting 470fps. Sweet...that must have been why it was shooting through peoples clothes....