I want explanation from SOE as a costumer about this.

I guess it's DX9 because Windows XP doesn't support anything further. And you might have noticed with the recent end of the XP Support, that there are still a lot people that use Windows XP. And you don't want to leave these potential paying customers (OP, see what I did there. ) standing outside in the rain.
So, if you want to blame somebody, blame the majority of people that still use Windows XP. As an example: The steam statistic for operating systems shows ~10.7% for WinXP around Feb. 12, ~9% in March 13 and even now there are still 6% that use it.
I can't say if the numbers truely fit the dates because steam stats are terrible and they don't track everything on a timeline. And that only shows the people out there that use Steam and send in their hardware specs. So the real numbers might be even more towards WinXP.

People who use an OS that is that's more than 10 years old, has no driver updates since a long time ago, no security updates and software constantly dropping support for it, that uses tech up to 2004's stuff on their rig that runs planet side 2 at playable frame rates (I'd say 2010 tech plus only) doesn't seem to be a big number, also just because that number of people has windows xp it doesn't mean they are magically going to run and want to play

I really wanted this post to be a discussion from an actual costumer :-(

Talk of seams and chafing or whatever. Oh well.