I think a big part of the reason Pokopia is hitting so hard for so many people is that we have had an absolute glut of post apocalyptic media that take the "humans are the monsters/disease/problem" angle. Even the most well meaning solar-punk I can think of often have this undercurrent of 'humanity's nature is inherently short sighted and exploitive and they must constantly be kept in check to protect the environment' which slides very quickly into 'the world would be better off without humans in it to complicate and threaten things'.
But Pokopia fully does not do that. The world is lonely without humans and lesser for humanity's absence. So much of the game is about how Pokemon miss humans and are struggling to make sense of a world without us, how the ecosystem is just as hurt by our absence as any other species, and how the things we left behind, even in ruins and burned shells, are often beautiful and strange and helpful to the Pokemon who find them.
Pokemon have always been this allegory for the natural world- back to the original idea of the games inspired by children who caught bugs and kept ant farms- and thus the relationship between Pokemon and humans becomes this allegory for the relationship between nature and humans. And Pokopia looks you dead in the eye and says "the world would be poorer without humans, and if we all vanished tomorrow the echoes of who we are and the things we did would still ring out for eons uncountable. We would be missed and mourned and searched for and the wound of our absence would be deeply felt on this earth for the rest of its turning. The actions of a few greedy short sighted humans will never change that."
