My thought is that we humans are bad (by computer standards) at arithmetic and memorization because those are not evolutionarily useful on their own.

On the other hand general problem solving is, and so far any attempt to replicate it using computer algorithms has more or less failed. So it must be more complex than just some simple heuristics.

Perhaps the answer is just "more compute" but the argument that "because LLMs somewhat resemble human reasoning, we must be really close!" (instead of 25+ years away) seems wishful thinking, when:

(1) LLMs leverage a much bigger knowledge base than any human can memorize, yet

(2) LLMs fail spectacularly at certain problems and behaviours humans find easy