>>57480734Said this in another thread but...
They've clearly decided not to do remakes anymore. Therefore, they need to remind kids that the Johto starters are a thing. And that's so they buy toys and merch of them. Similar for the Unova starters since they've both gone so long without the starters being selectable at the start of the game. So they put them into these games. Simple to understand.
The next Legends game will probs have a combination of Snivy (gone the longest without being selectable as a starter) and then a mix of Kalos starters (2013), Hoenn starters (2014) and Alola starters (2017).