It's a base factor that is correlated with popular success (financial success, to a creative type, is secondary, as long as they're making a decent living; the important thing is to have "lots of people watching your shit", as Trey Parker and Matt Stone put it). Increasing it is no guarantee, just like raising your child with excellent values and work ethic and a good school doesn't mean he'll get the Nobel or even do anything important with themself, but still, it's what you do if you want them to succeed as much as possible.

However, for the record, I'd argue that a show must be "good" for a purpose. There's no such thing as "good" in abstract. MLP;FIM was designed with the main purpose of attracting little girls and their parents, keeping their attention, and selling them toys. The authors made sure it was "good" for that purpose.