Euro.
I’m talking general trail bikes here, not racing machines. 6’2″ and over are usually on large or XL frames. From observation most seem to be sat very on top of the bike. Rather than in it. Take a look at a 5’10″er on a medium. Usually much more in the bike. A 29er will by definition have longer chain stays. So with the seat post up to the “correct” position the riders weight will more centralised compared to a 6’4″er on a large 26er, where the rear triangle and seat tube angle is the same as every other size in the range. Mass produced bikes and frames only change the front triangle depending on size.
As a frame gets larger the rear triangle “should” get bigger as well. People will argue that they like short stays because of manoeuvrability. But that’s on the bike that fits them. Not someone 6″ taller. It’s laziness and economics that bikes are built to standard sizes. How much would extra would it be for each size frame to have the scaled up or down set of tubes.
All of the above is just my thinking out loud and doesn’t reflect what people ride, find comfortable or prefer. I’m 6″4″, 33″ inside leg, long body and long arms. I have my saddle too low, compared to what the bike fit people say, and ride an 18″ medium with a long TT. 😕