I think they didn't want to pick Cheerilee because they already established them as "just friends". And any other mare from Ponyville would raise the question "why didn't this happen sooner?" Our Town was perfectly in that regard - newly integrated into Equestria, has at least two established, named mare characters. And one is a baker which gives BM an in with ingerdient-providing.
Also, I wouldn't call the Village four background ponies.