Not sure if I fall under the older players or the newbs who leave within 2 years.
I started on PvP on FAF over 4 years ago (was living at my old house), I played for a year or two regularly and then was playing other games for a time. I had played SC since release, discovering FAF and gradually getting into the PvP after a couple of years of just getting maps & mods. I did ok, could hold my own against most players of similar rank.
Came back and played some more the last year or so (the last 4 years my schedule also fucked my gaming as it didn't give me much time to actually play). Have only played a couple of PvP games, did ok, actually the last one I probably did really well - I got trash talked by another 1000 ranked player that I flat out punked on Gap of Rohan (we were Air on opposite sides, I hit him early with a LAB squad, followed almost at the same time by some bombers to screw his power, later on Mercy sniped him - asked a team mate afterward and he was ecstatic with what I'd done as I had that particular player locked down all game playing catchup from the early damage and removed him before he ever made a meaningful contribution). Thing is, 2/3 of the games I've joined you spend 15-20 minutes getting it together, and 3/4 of the time someone DC or leaves the game early because they screwed their build order and don't have the balls to just play it thru. Then everyone quits and you wasted what is now a half hour... To play a PvP game I generally have to figure I have over an hour I can spare with no interruptions.
Thus, I play against AI a lot, because I can pause, I can save, and I can complete the game. very frustrating to start a game to have to pull out early. Similar issues if you start up with the wife and are done in 5 minutes...
For newbs I think that it is a steep learning curve, I got beat, I watched replays of most games I was in to see what I did vs what everyone else was doing, and what worked and what didn't. Had a guy punk me once playing Rock on Setons, he was on the island from Beach before I even got a transport off. Replay told the story, after that I shaved 2 minutes off my launch time thanks for watching how someone else did it. The problem is, many people don't have that patience.
Second problem as I mentioned above, disconnecting players. It is extremely rare in my experience for someone to lose connection and get back in. In most cases a player disconnects it screws the team - though someone might inherit the units and economy, they also now have far more to task than before and for many players they can't suddenly take that on without dropping the ball in some fashion.