I mean really, apart from the homebrew stuff there's a decent amount of stuff that WotC are adding for their new edition. I imagine they probably want it to appear as close to the new edition as possible, so as to help with cross marketing and promotion. A lot of DnD crpgs in the past actually appeared using editions that were out of date compared to the ttrpg ruleset and I am sure they want to simply to focus on DnD so that it is as relevant when the new one comes in too
