For the people who don't know, I was a charter member at OSGeo since 2006, and I recently served on the OSGeo board of directors.
The main reason for leaving OSGeo at this point in time is that I feel that the recent communication that has been happening between OSGeo and LocationTech is very unprofessional and disrespectful from the side of OSGeo. I must say that Andrea Ross of LocationTech has been super professional, I'm not sure I would have been able to do the same in her position. This communication has been mostly on the conference_dev e-mail list (but also on discuss). It has been really hard for me to read that communication and not speak up publicly about it. I'm glad Cameron Shorter did say something about it here: https://lists.osgeo.org/pipermail/discuss/2015-November/015310.html on which I fully agree but I feel like a lot more people involved in OSGeo should have said something about this. I encourage everyone to read the relevant November threads in the archives https://lists.osgeo.org/pipermail/conference_dev/2015-November/thread.html and https://lists.osgeo.org/pipermail/discuss/2015-November/thread.html
The communication started just a few weeks before the final decision had to be made on FOSS4G 2017. 2 out of the 3 bids had chosen LocationTech to be their PCO. After all the communication on LocationTech as the PCO on the e-mail list I felt that they would never have a fair chance of getting selected for FOSS4G 2017. Even though the FOSS4G RFP doesn't say anything about not being allowed to use LocationTech as the PCO, it was clear that this was deemed a no go area by some of the people "in charge" of OSGeo. I feel sorry for the 2 bids that put in a lot of time and energy, and never had a fair chance IMHO, although ofcourse this is hard to prove. I don't want to say anything nasty about the winning Boston bid, since I'm sure they had an excellent bid, but I don't think the other two ever had a real chance after they made public in their bids that they had selected LocationTech to be their PCO (in other years, the name of the PCO was not always known in this phase). There is just no trust in OSGeo for LocationTech unfortunately.
OSGeo used to be an open organisation welcoming collaboration with anyone on their goals, but sadly it's not anymore. Also if you haven't read Darrell Fuhriman's post titled "OSGeo is becoming irrelevant. Here's why. Let's fix it." already I highly recommend it: https://lists.osgeo.org/pipermail/board/2015-September/013236.html