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It's a social game. The original marketing point of the game is to trade and battle with other people, and every installment (except arguably RS, due to its lack of backwards compatibility) has been expanding on it and improving on these aspects. RS has multi battles, which lets 4 players battle with each other, DP has Wi-Fi friend battles and trading and can connect to PBR for random battles. BW has random online battling ingame and a new trading system (GTS Negotiations) to spontaneously trade any Pokemon with another person. XY takes this and makes it much more convenient with the PSS, better breeding so more people can battle seriously, and Wonder Trading. SM creates Battle Royales so that 4 people can play without having to cooperate.
It's clear that GF's focusing on multiplayer in this series. However, places like /vp/ seem to only focus on single player in Pokemon, and only a handful of games in the series fill that niche, like BW2. The side series games are a lot better in a single player regard, and other series also pull off monster catching/using better in a single player aspect. Pokemon's best aspect is in being able to connect with other people and play with each other instead of doing things alone.