Are they actually rare? Why?

I want to attempt to complete the commons from the Baby Bella set since they are my favorite. But when searching to buy on eBay, from #1/92 until the #43/92, they are affordable and very available. But then when searching from #44/92 until #80/92 I practically don’t see them that much and when finding them, they are much more expensive. Can anyone explain to me why? And where can I find them? I would trade but unfortunately I am from Ecuador so it’s not possible right now :(