Well probably because most guys wheeling 40’s have been doing it a long time!
An experienced driver will be able to outperform and maximize the operation of the Cruiser they are most familiar with and probably as importantly, out trail ride an average driver anytime they switch rigs.
Driver experience is likely the most important when all rigs are similarly capable.
I think an average lesser experienced driver on most trails in a locked 80 is going to out perform most capable (locked, lifted, MT tired etc.) 40’s or 60’s operated by an average driver due to how easy they are to wheel and the margin of error they offer.
However, it’s larger size will become a disadvantage when things tighten up and can even be a challenge for a 60, especially on the trails you mentioned if they are as tight as I understand they can be in places.