Whne I first started I was quite confused by the boxes, but I've grown to like them. It adds another element of gameplay, I guess. Luckily they've relaxed on the box system a bit, and they usually give out free boxes in site events now too, so that helps. In a year of playing you can get 3-4 free boxes, which helps. But I can see how it bothers people, since it is an extra purchase.
I prefer it to sites who sell unique monthly items or pet colours though - that's not something I would spend money on, and it seems unfair to other players since it effects actual gameplay.