Maybe because most bronies eat that stuff up.
For Bronies, anything goes when MLP slapped on it, one brony brought a MLP colouring book and got a rage over it saying he was insulted by how "easy" it was.
That's why there are so many companies making brony shirts and other brony-specific merchandise with high prices, it's for all the gullible bronies, no matter how big the price is, someone will buy it.

Hell, I could get 20$ off this, and the buyer would be praising it and shoving it up his ass all day long crying tears of joy.