Readers were asking me about what was so bad about All Points Bulletin as game that it failed so miserably, and I didn't have an answer. I never played the game, which shouldn't surprise anybody, given that APB is a PvP shooter game. But I kept an eye out on reports which could shine some lights on that question. And I found this interesting analysis at MMO Tidbits which basically says that ganking killed APB.
Apparently by playing the game hardcore you would get your "rating" level up, which would make you deal 30% more damage and withstand 30% more hits than a new player. And some players used various hacks to make themselves even stronger. And then APB paired new players against those hardcore players, who would just mercilessly gank them over and over. Thus the newer players gained rating levels only very slowly, and pretty much lost every fight. As a result the server the author was playing on went from 2,334 players on a Sunday evening to 1,221 players on the Sunday evening two weeks later.
It is extremely hard to get somebody to pay for the privilege of constantly losing in a PvP game. And especially new players that start a game and always lose will often give up very quickly. This is why successful PvP games have safe spaces in which new players are completely or at least mostly safe from being ganked. APB didn't have that. It died of the fundamental incompatibility of MMORPGs with free-for-all PvP, where the "making your character stronger" part of the MMORPG clashes with the "only fair PvP is fun" principle. If you set up a PvP MMORPG in which players are actually rewarded for ganking newbies, you are doomed.