First a note - One must exercise caution in drawing conclusions based on polls like this. While it provides interesting perspective it must be remembered that the poll is skewed because it represents only that cross-section which visits these boards AND is motivated to vote in the poll. It's not necessarily an accurate sampling of responses. It MIGHT be accurate in its representations, but only by chance. What follows is just my current thinking. I don't pretend that it's any kind of detailed,
supportable analysis. It's more like thinking out loud.
The sixth leading factor is, "Publish more older edition material in parallel with 4E". Although I didn't select this, and didn't say anything about it in my post about my choices, I truly wonder why this isn't done?
IMO, it's because of a firm belief that support of more than one edition only undermines purchases overall. They don't see the purchase of a 1E book or PDF as anything but a LESSER amount of money than they could otherwise have gotten by selling the same person some 4E equivalent product.
It hasn't appeared that way to me until just recently, but such is now my impression. They won't say it but they despise the idea of selling ANYTHING that might support a previous edition instead of supporting the current edition. I think they had fooled themselves into thinking that they might actually be able to starve the holdouts into accepting 4E. That they would begin to play - and buy - 4E products if they stopped selling anything to support older materials. Where they miscalculated IMO is that 4E really has fractured the fanbase to a greater degree than was thought possible/probable. They produced an edition that simply alienated too many people. It's not that it was manifestly BAD, just that it was manifestly not a ruleset whose approach was palatable to too large a segment of potential consumers.
Dungeon magazine used to contain adventures from many different systems and editions, even up into the early days of 3E. I remember issues that had adventures for AD&D, 3E, and Alternity, all side-by-side - living in harmony within Dungeon's pages. When and Why did this change? Dragon used to have articles for multiple systems and editions also. I really loved the versatility and diversity both magazines had. It does seem as though something was lost when this changed. (I know that, technically, any material is adaptable to any edition, but not everyone is capable of doing this - I am, but many aren't.)
Those materials that were available for older rulesets into the early days of 3E were firstly materials that were still LEFT OVER from the TSR days. Also, some materials continued to be submitted for older systems. But once that was gone through and most players had migrated to 3E they had every motivation to cease any and all support for anything but the current edition.
At that time circumstances were on their side in such a decision. There was no OSRIC, Swords & Wizardry, or Labyrinth Lord systems to mimic the older editions and provide a foundation on which other 3rd party publishers could base support for out of print versions of the game. Even Hackmaster wasn't published until 2001, and that was probably allowed because they thought that the money from licensing the system would be worth the miniscule erosion in money otherwise destined for 3E. And at that time I think they were correct.
However, that was then. In the present climate there ARE a variety of 3rd party systems that mimic older editions including 3E via Pathfinder and it may be - MAY be, mind you - that cutting off everything to do with older editions is a calculated move that they hoped would result in dissatisfaction with attempts to find old/old-style materials and eventually bring more people into the 4E fold. But I don't think they anticipated the degree of dissatisfaction with 4E; that so MANY people would simply find it not to their taste. Accordingly, they were not prepared to properly deal with the unexpectedly heavy migration to other systems - whether to the D&D clones or otherwise. I suspect that their present posture is something of a knee-jerk reaction when things failed to go as reliably as they had anticipated.
Maybe.