@Dezaki The Youjo Senki chapters are also sometimes only about 17 pages. Go ahead and check for yourself if you forgot about those ones. Often the longer chapters of that on here also appear to have what might ordinarily be .5 sort of chapters rolled into them too, they're working off the volume releases and it's not necessarily numbered as a separate thing from the main chapters in there. Also, this and that are in entirely different publication sources. And then, to continue this chain attack against your stance, some monthly series aren't even 10 pages long. The magazine Seitokai Yakuindomo used to be in was monthly, but it's a 4koma and the page count was always low each chapter.
TL;DR: Variables exist, not all series are going to follow the same release conventions