>>43450770Immersion. It's the baseline and most straightforward way of interacting with owned pokémon, and even the limp way HGSS implemented them had a decently powerful effect on a lot of people, beyond the basic atmosphere enhancement it also made grinding new shit more tangible and less of a mind-numbing chore.
Had it stuck around in future games it would have made a great springboard for adding depth to existing mechanics or even new mechanics entirely, as well as better integrating features into the world like Amie that was a half-assed minigame on the side more than actual interaction.
All of that said, there's literally no reason *not* to have it given how trivial, simple and unintrusive it is. I don't understand why so many posters here get angry at the idea of more avenues for interacting with your own pokémon in a game about them.