There are billions of possible combinations of a cat, and breeding and collecting them can be fun in itself, so it actually has some entertainment value, just like other virtual props in online games
Throughout the game, the total value of all cats = the sum of the Ether topped up by all players, and the money you make from the sale of your cats must be the money that other players topped up in.
But unlike The Pyramid Game, because the whole cat breeding system is set up in such a subtle way that it doesn't preclude a small number of players from being willing to spend a certain amount of Ether and keep holding the cats - then there is actually still some value gain generated throughout the run of the game, and the value gain generated = the sum of the value of the cats that are ultimately willing to be held - but that doesn't change the fact that you want to make money, the vast majority of which is earned through a zero-sum game.