>>50226617Because Grass is a bad type period.
People don't want to pick a starter that will put them at a disadvantage when fire is a deent type and water is one of the best type in the game.
Especially when grass is weak to bug and flying, 2 of the 3 most common types in the early game of any pokemon games.
Drop the flying weakness and the resistance flying has to grass and it will make the type a lot more appealing for a starter. (also add in a fairy resistance because fairies are bonkers already)