I've noticed.. everything has Cheerilee. I think she's the favorite of someone at the company. I got stickers once. They had the Mane 6, Celestia, Spike and Cheerilee. She does seem like quite the random addition. For a while, she was also the only pony from the show besides the Mane 6 and the princesses to have a toy at all. Now they've added blind bag versions of some background ponies, but she's still the only one to have a brushable hair toy, and there's still no toy at all for characters like Trixie. Leads me to think someone with some power over product creation really likes Cheerilee.