Depending on your contract, proprietary vendors offer few choices about getting a vulnerability patched, if ever. If you're in the riffraff section (ie, most router owners only have a few), you might wait a very long time. One [1] from netgear that languished for months. And what about the Juniper backdoor: won't fix?
With open source, you can take the code to whomever you wish, fix it in house, offer a bounty, etc etc. There are plenty of houses that give away code and sell support. If GPL'ed, this model also accelerates fixes because everyone gets immediate benefit of everyone else's fixes.
http://betanews.com/2015/10/10/hackers-exploit-serious-unpat...