Also for the purpose of the game, the cards enable them to put out a ton of villagers simultaneously! To produce figures of all of them would take a really long time, and like the Smash series we'd see some of the rarer ones quickly become impossible to find without paying extra money to scalpers.
I agree that the reason for using cards rather than figurines is a result of limited storage and shipping constraints.
However I think the cards might be sold in packs of 5 or so with the intent of them being used like trading cards. It's an interesting gimmick as I interpret the cards as: The character cards will be moved between and traded with other players, just as how in game the character's themselves move in and out of your town to other towns.
Mayor Robsworth of The Beeches Manor