Why does everyone but ARMS make their BUIS with a quick release attachment system?  Think about it logically.  BUIS come in two varieties.  Fixed and folding.  You buy fixed if you don't trust a folding sight, and you want to use it on its own or with a red-dot sight.  They aren't useable with a magnifying optic unless you raise the optic over the sight line and then remove it to use the BUIS.

Folders are used if you want to get them out of the sight line for red-dot or magnified optics.  So now we get to my point.  Why do any of them need a thumb nut or lever so they can be quickly attached or removed?  The point of having a BUIS is to have it there, on the rifle.  Not pull it out of your pocket and slap it on.  In that single and limited scenario it makes sense, but for the other 99% of the time, it adds to cost and bulk.  Most of them put the lever or nut on the left side where it interferes with the charging handle access.  Even if it is on the right like the LaRue, it adds unnecessary bulk and cost.

If there is something I'm overlooking that justifies ALL the others being constructed this way, please enlighten me.

Thanks.

It makes more sense to me with respect to a fixed BUIS so you can remove it  to make room for a magnifier, NV, etc.  But if a folder is designed to sit low enough to allow accessories to clear it, then it does beg the question I guess.  Regardless, any BUIS that's designed for easy-off/easy-on needs to ensure reset to previous zero.

KAC is not QD.

Quoted: KAC is not QD.

Neither is Troy, or GG&G, or MI, or Cav-Arms, and the list goes on.  

The only one I can think of off the top of my head is LR, am I missing something else?  I suppose by a stretch one could call the CCH/LMT BUIS quick release because of the huge thumb nut...but it's def not nearly as fast as a throw lever.  And if you don't like the big thumb nut, you can just cut it off like many of us have done.

Actually, you guys have corrected me.  I was thinking mainly of the LMT and LaRue sights.  Should have thought about it more before engaging the keyboard.