Dragonhelm
Knight of Solamnia
1. Perhaps because in order to hang on to their copyrights they have to rerelease stuff every so often. Plus, don't you think they would have released the books next year to tie-in with the setting?
I can see this, though maybe the other Dark Sun series is scheduled for next year.
2. Since when did Dark Sun have a monopoly on Psionics. For all we know, the only reason they are in PHB3 not PHB4 is for Eberron's sake.
Dark Sun doesn't have the monopoly on psionics. However, when you mix the words "setting" and "psionics," Dark Sun is the first setting to come to mind. It was the first setting to thoroughly integrate psionics.
I was glad when Eberron started using psionics as well.
3. If you follow that logic, they wouldn't have released Eberron either, since it would compete with its 3.5e stuff.
There's a difference. DL was licensed, Eberron wasn't. Eberron would then come across as a continuation of the setting into a new edition. Dragonlance would appear (key word) to be taken away from the DL creators, who know the setting best. If WotC produces anything less than MWP quality in terms of story and continuity, there could be a backlash.
When you have the Weis & Hickman names attached to Dragonlance, that's hard for WotC to "compete" with. The 3.5 era of DL is considered by many DL fans to be the "golden era" of DL gaming. That's quite a legacy.
4. Neither does Dark Sun though...
There's another DS series, Tribe of One.