In reply to harold walmsley:
Interesting question. In general terms...
Accessibility: routes on the Outer Hebrides see fewer ascents than those at Stanage Popular
Seriousness: Serious routes see fewer ascents than safe
Difficulty: Harder routes see fewer ascents
Line: striking lines get climbed more
Quality: More stars = more ascents
Grade: soft touches get done more than tough for the grade routes
Traffic: Routes that are chalked up and clean, not overgrown, will get done more
Photographed: Photos of routes inspire people to climb them