Hasbro wanted to make money selling toys to the preschool girl "princess" market, and pink is a popular, "safe" color for a little girl toy. It's pure economics and has nothing to do with the show.
Came here to say this.
(Sorry, little rant about "girls toys" coming up
)
That's also the reason why Princess Cadence and her wedding with Twilight's brother was made into such a big thing on the show. Hasbro was planning a wedding set because gender stereotyping has made girls and young women
obsessed with that kind of thing.
From an early age girls get told that the most important thing in life is "finding your true love", marrying him and - at best - having a bunch of babies with him.
Also weddings should be only about you, not your lover, you get to wear a nice dress and be the center of attention.
Weddings get marketed to little girls like war gets marketed to little boys. If you think about it, it's a really manipulative and sexist thing.
And of course they had to create a new character for that wedding set. One that would fit the love theme perfectly - Cadence was created. And of course she had to be pink and her power had to be "love" - and yet
another "princess" character.
Now I'm not saying that the wedding set is horrible or the wedding episodes were horrible *g*
In fact I really liked the wedding episodes and I also have nothing against Cadence (even though I think her character design is
really over the top).
Little girls wouldn't love pink that much, or weddings, or whatever - if it wasn't so shoved into their faces by society and toy manufactures.
So with Cadence being a canon character now, Hasbro probably felt it was "safe" enough to finally make a show-accurate Celestia.
Btw, little girls are not stupid and they surely must have realized that the Celestia toy didn't look like the Celestia they knew from TV. Just because something is pink doesn't mean girls will like it better.
This clip is probably well-known by now