Google+ is an old timer and probably doesn't need to be reminded. He knows it's full but he still tries his luck. You don't need to remind them every now and then.
Not only that, but you could probably make 50 posts per week writing the kinds of posts OP wrote. Members do what Google+ did in campaign threads all the time (at least they were doing it before I put the Services section on ignore, but I'm assuming things haven't changed much). It's not worth your time and effort to respond to an application, even if the campaign is clearly closed, the member isn't qualified, etc. They're probably not going to read what you write anyway.
OP, yours wasn't a low-quality or spam post, but it was probably reported by someone who didn't want the campaign thread to start having a bunch of posts that clutter the thread. If a campaign manager is looking at his thread, I'm pretty sure all he wants to see are applications and/or relevant feedback to the campaign.