Right now we got M19 which isn't even in standard anymore. Before that we had Ravnica sets which will rotate the soonest. When was the last time we had M20/WAR/Eldraine when they weren't the most recently released set? It's kind of hard to interpret this as anything else other than "we don't want people to have a chance to draft a format that will have legal cards in standard for years".
I don't mind that they sometimes don't have current set in ranked draft, but it doesn't seem like the rotation is evenly split at all.External link →
The primary reason is that when we are close to rotation (e.g. after M21), we don't want to be running draft formats that will soon be rotating out. In order to keep the cycling-format drafts have a variety of sets, we're more likely to run these formats now, when rotation is not soon.