>>1824059
It's more that the human organizations are the ones making a bigger effort to explore the world.
The first game, Blight is in Vaeltria, that is a mostly human country, so the cast is more girls than monsters.
The second game, Awake, is in Palgadol, the monster country, so the cast there is nearly all monster girls.
The third game is where that part of humans exploring the world kicks in as it happens in Schisma that is the Island of Pests, but when you get there the country of Alzhetts had already deployed a knight force there etc.

The collab is using mostly Blight girls so two of their human girls and the sole monster girl in the party, Nyx, as well as two popular girls of Awake, Nazuna and Maria.
They could have easily gone with a full monster girl cast instead but I guess they really needed to put girls from the first game first since it'd be a shock if people went from there to try SEQUEL and learn most of the units are in the second game.