Companies want money, if a product already gave them money, then a sequel have a chance of success guarantied. It's hard for a company to venture in something new because they are always afraid to lose.
Smash is great, the first smash had a awesome statement, and Mele improve everything. After this I feel it was done wrong with Brawl. The same it can be said of Mario Parties, which are entertaining, they are bad compared with the previews one.
Also, it's easy to remake or port to a new console a old game that sold well in the past, because you know its easy money, and this is what companies want. Reason why with the time indie developers are having more and more importance, because they have nothing to lose, so they can do what ever they want.
Some developers are getting aware of this (like the creators of Halo) and they have force them self in trying to do something new and stoping doing sequels and prequels. But sadly the big bosses of the companies are the ones who manage everything, so big companies as square enix, capcom, and others are going to lose their credibility, while new ones are going to gain their place in the gamers heart.
Also, Nintendo is the Apple of consoles.