It makes sense for an amateur to think that, yes. Optimism is fine, but do it for the love of doing it, not to make money. Because the odds are stacked against you making any.

taby said:

You might have a hard time keeping the art direction consistent, but other than that… why not?

By relying entirely on free assets, you are basically saying that you don't even care enough about the game to invest a few bucks in paid stock assets. Good free assets exist, but enough of them in a consistent style for creating a full game? Not likely unless you're going for a very short, very generic game.