At the beginning of battle, BB players keep shooting the small islands. Once the small islands are taken, you as APA cannot gain any exp from occupying it.
Then as battle goes on, there are 2 possible outcomes.
1. your team lose. If this is the case, likely you will get 0 attack, and you receive 0 exp with 0 attack.
2. your team wins. In this case your team's BB will start to shoot enemy main base before you can even reach there, and you get no chance of landing on enemy base for any exp. If you try to rush before your team's BB start to attack base, you will die from enemy fire. And with no enemy ship around you have no chance to attack anything, thus still no attack and no exp gained.
And not to mention that, everyone loves shooting APA. BBs love shooting APA instead of shooting enemy BB (even if enemy BB is shooting them and your APA is harmless), SS love torping APA instead of fighting other ships (even if your APA runs away from them and that SS is being attacked by other ships), CVs just keep bombing the s**t out of your APA even if there is another damaged BB5/6 nearby and it will receive much more exp bombing that BB (OH HELL! ESPECIALLY WHEN YOU ARE PARKED NEAR THE SMALL ISLAND! I get bombed EVERY TIME when landing the small island, with no exception)...
As APA driver, you actually receive more exp in GB than in the f***ed up Occupation mode.