It was poorly planned from the beginning, or planned by someone who had no idea what they were trying to do and padded a resume with things that they didn't understand to begin with making promises of things that could be done with no reasonable understanding of what it takes and timeframes of getting things done and publishing.
Considering this isn't hypothetical, but an actual person is behind these things, accusing that person of padding their resume is just a wee bit rude, but maybe that's just how my Mom raised me.
Plus there's the fact that (at least last I heard, in all fairness I haven't been reading it lately) Chris Young was in charge of Dragon and Dungeon online, and having done a tour of duty at WotC and then Paizo on the magazines before going back to WotC for a few years, I'd say he wasn't padding his resume and does have a clue what he is doing.
However, your entire argument is based on the premise of "you should be doing everything months early, so nothing can be a problem at all." Well, that's all well and good in theory, but theory meeting the real world isn't always that easy.
A) We're only human. I should have started saving for my retirement when I got my first part time job on high school, and I should brush AND floss after every meal, and a whole lot of other I shoulda's that just ain't true.
B) Probably more of an impact in the case of Dragon and Dungeon is that it is in addition to everything else that WotC is doing. In your explanation, it's easy for an editor to tell one of the people in Design "Hey get me that druid playtest article by such and such date." However, that designer is also working on other projects, and WotC has even stated (or at least did back when I was reading eDragon) that if a Designer has to decide between working on a print book or an article for DDI, sorry, but DDI can wait. So an editor can happily assign articles all he wants, but if the resources to get them done aren't there, it doesn't matter at all how far in advance he assigns them.
C) Freelancers flake out. Unfortunately, I know I've been responsible for that as a freelancer (sometimes with good reason - wife's cancer during Oathbound; sometimes without good reason). An in house person is easier to hold accountable and keep them on task, but as with B, they often have a dozen other things and not enough time to do them all. Freelancers, on the other hand, can be just as unreliable but for less obvious reasons. You say "if they miss X deadlines, they never work for you again", and that's really easy to say. But realize that every value of 1 to X, means your schedule slips. Sure, most magazines start working very far in advance, but slippage will eventually get you to tight deadlines no matter how hard you try.
Oh, and advice like this:
You can commission two peices of work, one from different artists if frelance, or inhouse have difference artists work on the same thing, and the unsed can be trashed or saved for later in an archive of unused artwork. This reduces stres for not having anything even when you would have prefer the one that wasn't quite finished, but didn't want to rush and end up with faulty art like Erik described having a fighter wielding a vagina.
isn't all that helpful. Sure,
doubling the art budget can help you meet deadlines and handle problem art, but try selling that idea up the chain of command. Sure you can say that some can be used for later projects, but that's still cost today for something later (very hard sell), and also pushes for more generic artwork that is easier to re-use rather than artwork more directly tied to the article.
I have only freelanced with magazines, but from that little experience as well as just listening to those who are in the trenches every day talk about the experience, I'd say that your ideas are great in theory and of course every publisher should aim towards them, but in reality, things are usually far more complicated and difficult and your ideas are best as a goal than expected practice.