The japanese blogger/interviewer Matsumiya managed to meet Masuda at Pikachu Outbreak 2019. He talked a bit with him and managed to turn the conversation into an article.

>Junichi Masuda: At some point, Pokémon wasn’t that popular.
>Matsumiya: Eh? It wasn’t? I played pokémon games on Nintendo's handheld console, you know. But I thought it was always popular?
>JM: No, it was different back then. I thought it was good at the beginning of the series, but then it became less popular, and I thought it was bad.
>M: When was that?
>JM: Around the time Pokémon Crystal version came out. Once Pokémon was about to move to the Game Boy Advance, there was a break, in the production of the games. I wondered if the player would think, ‘Oh, so this story process will just repeat itself.’
M: That’d be useless?
>JM: It would be useless if you couldn’t feel the harmony and excitement of the pacing, because in the game, the number of pokémon had increased a lot.
>M: Ah, right, at that time the number of playable pokémon was around 250, right?
>JM: Right, so I had the next couple of games set in a far away region from Kanto, Hoenn, in order to both reduce the links with the past and reduce the number of pokémon in the pokédex, in order to keep things simple. But even so, even when I tryed to not repeat myself, like with Pokèmon Black and White versions, pokémon still was less popular. It continued this way until I figured out how I could bring it back by removing certain features and keep simplyfing the games.
>M: Even so, how did you come up with the idea of steamlining gameplay?
>JM: I studied other popular game series, like Puzzle & Dragons[laughs]
at the end of the day: ''Creating a good game isn’t as important as making a game that lets people have fun''.