Because body-building is an art form, not a form of exercise. I have worked in physical jobs that require overhead lifting (for example) and, regularly, scrawny-looking guys have to help out their body-building cow-orkers, who just haven't developed the ancillary muscles that provide control and balance, because that loses "definition" (or whatever the term is).

>There are professional climbers who are 'heavy'.

Who? The heaviest I can honestly think of would be Chris Scharma, Magnus Midtbo, Jimmy Webb and maybe Jan Hojer, but all of them would be considered pretty skinny by normal standards. Scharma and Webb are probably around 6' 160-170 lbs, Jan is around 175 I think but he's 6'3", and Magnus is 5'8" and 158 lbs or so but has incredibly strong fingers.

Climbing is a strength to weight sport, so being heavier will almost always be worse than being lighter no matter what. It's why you don't see as many tall professional climbers as you would expect.

I put heavy in quotes, perhaps I should have put professional in quotes too.

Here is a larger climber who is sponsored by a lot of climbing companies: https://www.instagram.com/drewclimbswalls/?hl=en I'm not sure the extent to which he might be considered a professional, but having multiple sponsorships suggests it's semi-professional for him.

He's not pushing the limits of the sport, but he's promoting a more inclusive attitude. Climbing for a lot of people is about having fun, and very few people will send the hardest climbs, but you can be professional without being elite.

Frederic Nicole: 180 lbs

Klem Loskot: 190 lbs

John Gill: 200 lbs

However, None of these guys are performing at a top level today, none of them have sent V16 or higher. Gill is the father of bouldering in America, and was setting standards from the 50s-70s, and claims the hardest problem he has done was about v10, at a time when no one else was anywhere near that good. Bouldering was a lonely pursuit in those days. He was able to hold one-arm levers and do one-pinky pull-ups.

Gill was also plagued by tendon pathologies in his elbows throughout his career, and those issues are more common amongst heavier climbers. Don't let that stop you from trying climbing if you're heavier, amongst mortals it's not such a big deal.

I have never rock-climbed, only briefly messed about enough to know it's not happening despite my pull-ups peaking with +50kg added weight.

The "not happening" was that my weight distribution feels like it was ripping me off the wall. I just can't get much percentage of my bodyweight supported by my toes because my big back, ass and quads are going in another direction. Turns into an upper body exercise and one-arm pull-ups on a sheer face aren't happening.

If you feel like your weight distribution is ripping you off the wall the problem is learning how to manage your own weight distribution skillfully. Your big ass and back is a benefit here; these will maintain your core tension necessary to keep position. You were probably ass out instead of hips against the wall, which unbalanced you.

It's most likely just climbing technique, keeping with it for a few more months would have yielded pretty good results I think.

While not a pro, the fat old climber is far from the typical body type. https://explorersweb.com/fat-old-climber-gordon-robb/

Strong people that start climbing tend to use their upper body strength to get up the wall, fat people don't have that option and naturally fall into using technique and their leg strength to get up the wall.