Most people shy away from odd-sized cards. Topps Big and 1989 Bowman don't fit in normal pages properly, and they were fairly large releases. And Topps' mini cards don't do so well either; the tobacco minis have dedicated pages but those other minis can be tough. And then you can add in other oddballs - postcard-sized cards, round cards (Fleer Hardball), Goudey, and all of those other odd releases from the past.
I love that stuff, though. I want all the Topps Mini sets from the 1980s and the recent throwbacks too. I have the '89 Topps Big set. They're not the easiest things to store with the rest of a collection, but they are fun to have.
And when it comes to Japanese cards, "standard" card size didn't really arrive until the 1990s. In the 1960s, many menko cards were standardized to a "tobacco card" size, but with their extra thickness they are still a bit big. Add to that some great die-cut menko and plenty of round ones, and you have a lot of variety in card sizes, even in the past 60-70 years. (To put that into perspective, Topps issued its first major standard-sized card set 60 years ago.)
Given that the set includes four different-sized round cards, my guess is that the "set" was printed on a single sheet. This is purely speculative, but makes some sense, because many menko sets needed to be cut or punched out from a full sheet.