This is more or less my take, but at least for me it's not about the level of difficulty exactly. It just feels very transparently like exploring a state space, where the "a-ha" moments just boil down to breaking into a different neighborhood of that space. To be clear, the puzzles are very well designed, and also very hard; but I don't find solving them satisfying at ALL. Compare with Baba Is You, where the "a-ha"s feel to me more like having a grand insight than finding the right very specific sequence of moves.

Put another way, it's been years since I played Baba and I can still remember the key insights to some of the sneakier puzzles. I couldn't even begin to do that for SSR.