They are trying to simultaneously manage the revised editions of the three core rulebooks.
I am willing to bet that whomever was working on
Eve of Ruin was not ONLY working on
Eve of Ruin. Every single D&D designer, developer and producer was/is probably on several different projects all at once in various stages of development, having to go from meeting to meeting, product to product, trying to push every single one of them forward on their conveyor belts. So the idea that WotC has these editors sitting around that will have the time to spend several weeks doing nothing but stripping the entire 150 pages book down to its roots and making sure every single bit and bob makes logistical and logical sense against every other bit and bob in the book is probably a bit unrealistic.
Yes... a single individual or two for a small indy company who are only working on their one project for months/years on end can edit their adventure down and hopefully tie everything into a tidy bow. Which is why more people
should be buying those adventures, rather than poo-pooing them and stating that they're "probably unbalanced" and "probably aren't playtested". Better that, than wait around for WotC's books to get released... only to find those books as "probably unbalanced" and "probably aren't playtested" in their opinion.
People keep thinking that bigger companies should be able to make the same things smaller companies do, but better and cheaper. But that's just not what increasing size and numbers actually does. More people means more logistics and more opportunity for small things to fall through the cracks.