Let's face it:
MLP is and always was a series to boost sales for a "girl toy". The huge mature fanbase sure was not really planned, altough G4 sure put a lot of effort into making the series enjoyable for adults, too. Let's just say that the little girls cannot really afford buying a lot of pony-stuff, but their parents sure can and they will be more likely to do so if they also enjoy the show. And having an own show may also generate money, let's just think about advertising income. Figures.
You have a peaceful place where everyone is friends, most adversaries turn out to be just manipulated or otherwise originally nice and benevolent ponies/creatures, friendship is a huge thing, bullies always fail on the long run, 90% of the population is female, there are a lot of longe manes to be combed and styled, fashion also is a huge thing, magic is present and in the end there is always a happy ending. Always. Oh, and there are princesses! And they all are ponies! Astonishing!
Btw. back in the 80's and 90's we had Turtles, He-Man and what not following the same principle of promoting a major line of toys, just for the other gender. Everything perfectly shaped to suit the target audiance.
And speaking of fashion, what does the vast majority of little girls crave when it comes to that topic? Shiny, colourful, sparkling things! Gold and silver are fine, but kind of boring. Ever the same colour, no glittering, just plain metal, although fine crafted. But you can't have jewlery without jewels, so gems are urgently needed! They sparkle, they are colourful, they can emit shiny rays of light and, AND magic! Ever imagined a perfectly crafted heartshaped man-high piece of marble? Compare that to the same, but made of crystal ant the like. I bet I know what will get more attention from the original target audiance...
Just my 50 cents,
Dennis