This is a quote that I remembered from DDO Gamer.
[09:50:08] <%SteelStar> As far as I'm aware, the DDO UI elements cannot be resized by any means right now
[09:50:57] <%SteelStar> Pretty sure the long and short answer is "Devs did not anticipate 4k resolutions in 2005, when the average was still 800x600"