I think it's as simple as this....

The longer the board is around the more "old timers" you have. A certain percentage of those people just as our real life "old folks" will get progressively more and more bitter as time passes...lol. They then get mad at the newbies and so forth.

So the longer the board is around the more oldtimers you'll have being irritated by newbies.

I'm pretty sure that's a good chunk of the problem.