I don't know. I'm just on the end-user side. Just a guess from my (pretty limited) understanding of the issue: The grsecurity[1] patch includes PaX[2] that can break a lot of software. e.g. Java and X11 and there are sometimes other unwanted side effects as well. And I've found a blog post stating that the author does not want to maintain a upstream patch[3].
1: http://en.wikipedia.org/wiki/Grsecurity
2: http://en.wikipedia.org/wiki/PaX
3: http://www.corsac.net/?rub=blog&post=1535