User blog comment:Deathstalker666/Vorknkx's Level Resources/@comment-1496755-20170103003016

So, there is a clear trend here - you have found a lot of WAST and Simple maps, yet nothing from COLLECT1, which isn't even on the list yet. E10N and Little are also very underrepresented.

If you being strictly chronological, this could explain it - WAST and Simple were probably made earlier, with older WADs, while the others used newer stuff.