OK I have a question, why is bouldering more physically intense?

Much much shorter height, so there's no endurance element -- it's purely about strength, power and technique (not necessarily in that order). As you noticed, you're almost never going to find a rest point in a bouldering problem; it's very, very anaerobic.

Think doing Tabata intervals versus marathon training: it's not that one is intrinsically more difficult or demanding than the other, but the former is going to wreck you in a much shorter time. *g* It's that sort of compressed intensity.

Also, when you're doing roped climbing, you'll usually be taking turns belaying, which means there are natural long breaks when you're not climbing yourself. With bouldering, you can keep throwing yourself at a problem again and again and again; often people will end up taking turns on a problem (and having lots of tea breaks), but the pattern is more one of lots of very short bursts of intense activity.

Obviously, you can boulder gently (e.g. doing lots of problems that are easy for you, maybe as a way to build endurance or just have a light day), or do roped climbing very intensely. But I did say "tends". *g*