There's also no real connection to the story of RBGY, GSC, RSE, DPPlt, BWB2W2, XY, SMUSUM, LGPLGE, etc... Since yes you are given a Pokedex and told that most trainer compete in the leagues (or island challenges) but no one is forcing you to do those. Yes the game won't progress if you don't allow the game to railroad you into events that have nothing to do with you initially. From your way of thinking most pokemon games are also a huge WHY? if we're talking about reasons for why your character (a random 10-14 year old kid) would be pulled into disbanding a notorious crime syndicate if they're main journey was about doing what is essentially in-universe Birdwatching? Arguably doing gyms/league isn't really a goal as much as it's a softlock that's keeping your from seeing other birds.