>>32658222When the cities have features interesting enough to warrant returning to them during the playthrough, it makes the region seem far more full and alive.
Backtracking when it's you who has to figure out that's what you need to do to proceed. "I wonder if that gym leader has come back to their gym after going missing." "I wonder if this construction is finished now". The fact that you go from hypothesis to discovery generates positive mental feedback. It's like solving a small puzzle.
Also, if Fly hasn't been learned yet, you can't help but try to solve a route backwards from what you remember. This is using memory and spatial reasoning to generate your hypothesis.
Watch Mark Brown's YouTube channel about game design. If you think about what games make you do too literally you may as well ask why most games exist at all if each individual step in a game is not super challenging.