Well, because dropping the gas or upping the buffer weight only delays unlocking so much and people are trying to figure out how to delay it longer. It would seem, no? And I don't think you need a proprietary buffer tube, spring and buffer for the LMT BCG do you? Or the BCG in the OP? Or the Surefire OBCG?
I'm interested in this as a way to get a quieter suppressed AR with less gas. I'm not sure that it's a real solution yet. I do agree optimally gassing the rifle should be a shooter's first step before anything else. And I suspect that the benefits of these alternative BCGs are really diminished once the gas is adjusted. I have limited experience with these type of BCGs. I tried a KSPEC on a rifle that was severely over gassed. I tuned the gas port and made it much smoother, less recoil and ejection port gas, and a tad quieter. Then I dropped the K SPEC BCG in. I was pretty disappointed but I suspected all along the difference was going to be super negligible. I think a person would have a hard time telling any difference between the KSPEC and a standard BCG in a well gassed gun. So maybe it's the same situation with these delayed unlocking, elongated cam path BCGs. But maybe it isn't. Having less opportunity for gas and sound to escape the ejection port would be cool. If the Griffin side pocket BCG demonstrated a noticable difference (in an already properly gassed gun)that eliminated a substantial amount of gas and was quieter at the shooters ear, I would commit to a proprietary buffer tube, buffer, and BCG. My only issue would be the cost.
Honestly, I may be mistaken about the proprietary parts with regard to the subject of this post. There are, however, other BCGs that seek to do the same thing, that are comprised of proprietary parts.
I don't quite get what you mean by either the buffer or an adjustable gas block only being able to increase lock time by so much, implying that the BCG can increase lock time beyond what can be done with another method, while still having a running rifle. Either buffer weight or an adjustable gas block can be used to increase lock time to a point where there is no longer sufficient pressure to operate the system.
Still, there is such a thing as too much closed bolt lock time. The longer the bolt stays closed after a round is fired, the lower the pressure available to cycle the action.
Again, taking the example of the properly gassed rifle that runs well on a standard buffer and spring. Now, take that rig and drop in a BCG that increases the closed bolt lock time. What happens? By the time the bolt unlocks, there is likely no longer pressure sufficient to cycle the bolt with its existing mass. So, what do you do? Reduce the reciprocating mass and/or spring rate/tension? I can see this having a negative impact on reliability as the rifle is fired and gets more and more dirty. It will get to a point where the buffer mass and/or spring no longer have enough umph to peel another round off of a fresh magazine.
If you look at it from the opposite side, with a severely overgassed rifle. Say an 11.5 with a .078 or .080 gas port. You're getting stuck cases and the rifle is beating itself to death. In this case, I doubt that the lock time added by this BCG will fix the problem without some help from either a heavier buffer or adjustable gas block. In this case, you could have just omitted the BCG with the use of the other two items.
The only point I'm trying to make is that this BCG being discussed would likely do well with a slightly overgassed system, but the solution isn't worth the expense when you can get the same result with a $200 riflespeed and/or $30 buffer, while getting a lot more flexibility.
Still, what would be interesting to see is if you take, say an 11.5 with a .070 gass port. Perfect. But then you throw something like a Polonium or YHM Fatcat on the end of it for a dedicated suppressed rig. Will this BCG delay the unlocking enough to rein in the added pressure and do something about the gas face. If so, this BCG may be a good option without having to mess with an adjustable gas block.