If You Could Change a Pokémon...

[prog rocker]

Well, Wobbuffet is in basically every game because of the TRio's own Wobbuffet. They sure as hell don't want to pull another BW and leave him behind due to it not being available in the region. It's essentially the same reasoning as to why neither Meowth nor Pikachu ever get excluded from any games: these 3 are pretty much the ''3 Constants'' of the anime when it comes to Pokémon, since it's basically guaranteed they will appear because of the TRio and Ash, so, they are always there.

Meowth had a break in Hoenn and Sinnoh, too.

 

[Norzan]

You can technically get a Meowth in Emerald by trading a Skitty at the Battle Frontier, and in DPPt you could get one in the Trophy Garden.

 

[prog rocker]

I don't really count them since they are pretty much post-game.

 

[Bolt Strike]

I don't really count them since they are pretty much post-game.

Then by that standard Meowth was only in 4 regions, and appeared as a regional variant in 2 of them. Meowth was not in the main game in Hoenn, Sinnoh, Unova, or Kalos. Wobbuffet's had a few absences itself, it wasn't in the main game in Sinnoh, Unova, or Alola. As important as they've been in the anime because of Team Rocket, Meowth and Wobbuffet haven't been all that frequent in the games, so this notion of "they have to appear because anime" doesn't really hold up.