Take these, for example:
My grandfather never went to Spain, never saw a bullfight, wasn't at all interested in bullfighting, and yet he had maybe a hundred matchbox labels with bullfight pictures on them. What he was interested in was matchbox labels. As you can see from the haphazard ordering of just these few, he didn't buy them as sets, he just put them into his collection as he came across them.
Bullfights were controversial even back in the 1970s, and probably more so today. There are people who are passionately in favour of them and people who are passionately against them. As it happens, my younger daughter knows someone at work who (rather inexplicably, as she's not Spanish) falls into the former category, so I'm offloading 80 of the bullfighting pictures onto her; the remainder are spread sporadically through the collection and I'm not going to hunt through pages and pages of Spanish matchbox labels to locate them.
Ironically, as bullfighting is controversial, I could probably sell these for more than the usual pittance on eBay. Oh well. It's not as if I was going to try flog them to random bullfighting fanatics anyway.