Why are successful human rock climbers so dissimilar to Hominidae primates who spend extended time periods climbing?
As a rock-climber myself I’ll attempt to answer:  The selection criteria for competitive rock-climbing is exclusively based on sustain non-resting, extremely challenging moves up a rock-face.  The two most challenging aspects are 1) ability to ‘crimp’ (climbing term) on micro-holds without slipping and 2) being able to keep that up without resting throughout the climb.  I personally have a real problem with the later, because of my weight.

Primates selection criteria is not isolated to non-resting climbs.  They don’t get penalized for sitting on the branch.