About Casual and Hardcore Gaming...

A short answer to your question would be "it works" or "it makes the most profit."

That. Look how well some shovelware sells. High School Musical 3 for DS sold a few million if I remember correctly because of all the HSM hype. Also, it's dependant on the console. Look at the GBA before it died - the charts were full of shovelware, with a couple of Pokemon games. Not a good example, true, but it's a point. Some of these games were rereleased too, such as Scooby Doo and the Cyber Chase, which was in the charts for a while, left, then was rereleased bundled with another game.

I think we're getting into the dangerous "Licensed Franchise" territory . Unfortunately it's not just Nintendo's consoles who've had to suffer - this has been happening since the Atari 2600 (E.T., anyone?). Yes, there are some phenomenal exceptions when developers put the effort in (Goldeneye, King Kong, Ghostbusters, etc.), but either the concept of the franchise doesn't translate well into to video game medium (There's a PC game for "Dirty Dancing" for feck's sake!), it's rushed out to coincide with a film's release date or the developers simply don't care about the franchise (To be frank, I'm sure I'd put little effort in if I was forced to work on a High School Musical game ¬¬).

I think in terms of both casual and hardcore video games (hell, this falls into ANY medium really), it's more about securing a profit than originality/creativity - Why experiment with some unknown formula when you could play it safe and emulate something that's been proven to work?

The problem with licensed games is that there's often very little time to make it. Recently, games have been given more time to develop, but for things like GBA games only had a few months to be developed.