I suspect part of the problem (for surfing) is the absence of a clear line-up. It's not the wait that bugs me, it's the constant maneuvering (and physical dangers of collisions in the water with boards). If I could join a clear defined lineup, wait my turn, paddle into a wave that I knew was mine to take, get a nice long ride, and re-join the lineup, I'd be fine with it. That there is such a thing as a line up at breaks with very well defined take-off zones, but even that breaks down pretty quickly in a crowd. A small number of surfers can make it happen, but good breaks in an accessible place (certainly everywhere in Santa Cruz) will exceed this crowd size 98% of the time.

I'm not a climber at all, but I've done a little bit of climbing on an indoor wall, and a crowded day means you need to wait longer, which is a hassle, but I get the feeling there's a much clearer sense of how to wait for your turn, with less interference when it is your turn. No idea if this is the case for outdoor climbing, though, or at more advanced sites. I'd still prefer a less crowded day with shorter lines of course - but crowds on a surf break don't just make it take longer to get the experience of a ride, they can pretty well ruin it. That's a big part of why I only surf uncrowded beach break.