Whoa, that is very strange. Do you have any insight into or even guesses at the reasons?
So... there were really 2 reason why Boost wasn't accepted as a mentoring org this year. First, GSoC was trying to bring in more new orgs, so there was more competition. So, if you didn't have a stellar set up, you weren't as likely to be accepted. Second, our proposed projects list was disappointing. There were really only two specific project ideas: one for Process and one for Polygon. Obviously, that's not making the cut. I think if Boost community wants to continue participating in GSoC, then we have to be more pro-active about documenting project ideas. If I had to judge, based on the amount of feedback I got this year after soliciting proposals, I'd have to say that the community isn't very interested in participating.