>>48690673For whatever reason DP Sinnoh decided to spend a decent chunk of its dex slots on unimportant parts of the game (honey trees, ocean pokemon in a region with abundant water types and 2 sea routes, etc.) instead of places the player would actually spend time in.
>>48690341In theory, regional dexes give GF more control over the player's overall experience (would the Magikarp salesman have been as memorable if the player had easy access to other water types before Cerulean?) and help define the basic flavor of a region and its individual areas. It doesn't always work, of course, but that's what goes through their head when they're planning regional dexes out. (You could also argue that it's to encourage trading or transferring between different games, but that doesn't answer why almost all games have significant overlap in their national dexes.)
