I think the reason is that everyone shoots lighter recoiling guns better. Plain and simple. I have one installed on my 25/06 not because it kicks, but because it brings it down to .223 levels to where I can see the bullet hit in my scope. Also it helps at long range where you can spot your hits/misses etc. All in all, everybody shoots lighter kicking guns better. I think anyways.
On the 6.5-284, if used for 1K BR, guys want to run their rounds as fast as possible normally with little bag upset, that is why the muzzlebrake.
As for the different configurations, if you are talking about chambers you will find most shooting .290 neck with minimum SAAMI chamber, 1 1/2 lead and throated for particular bullet with 28-30" 1-8 twist barrels at 2900-3000 fps, few using 1-9 twist. About 10% percent are shooting some form of an improved case and overall same dimensions other than improved and maybe 3050-3100fps.