because as travel increases more and more compromises have to be designed into the frames to allow clearance for the wagon wheels.
it also comes down to their respective uses, big wheels for fire roads and and the occasional small bump yes by all means.
every long travel 29er i’ve tried was a barge, you don’t so much ride them as wrestle them.
to recap lots of inertia in a straight line = good thing
lots of inertia and deviating from straight line = bad thing
why do you think big wheels are everywhere at XC events and almost non existent at gravity enduro’s and downhill races?