>>58003121Game Freak does not want nor put the effort into letting players obtain more legendaries through breeding or other repeatable methods, yet at the same time they make them version exclusive, let them in official tournaments, and still want them catchable in later games without the need for transferring.*
It started in Platinum. Back then, they were just scattered about in the region. For some it felt out of place, but there was an effort into giving them some cohesion with the setting than what came later.
ORAS's Mirage Spots were the shifting point mixing both old and new, and as of USUM, all this backtracking converged into whatever gimmicky feature they want to dump in, leading to legendary landfills such as Ultra Space Wilds, Dynamax Adventures, Ramanas Park, and Snacksworth. I would not be surprised if this happens again in Gen 10's DLC by either having Snacksworth return or making yet another dumpsite.
*Referring to legendary Pokémon as a collective. There are exceptions to each scenario.
>>58003395I consider it the prototype to what we got ORAS onward.