Because if it wasn’t that spec then it wouldn’t be picatinny.
And it doesn’t matter how wide the slot is, you should slide the rings forward in the slot until contact so that there is no empty space in front for them to slide to under recoil.
It's 2025. I know people are worried, with all the arguing going on online, we will run out of commas and periods. I assure you there are still plenty, people don't need to ration them.
Vortex pro rings are made to fit weaver or picatinney bases. The slot in a weaver base is not as wide as a picatinney base.
The lug to slot slop doesn't matter because the lug gets pushed forward until it contacts the rail.
Completely normal. There is always a little play with any ring/mount. As mentioned a few time you push forward so the cross bolt in the ring is pushed up against the rail so under recoil there is no chance of movement and then tighten. It’s simple.