Re the statistics, the key here is a concept called survival bias.
There’s this story about how in WWII they tried to make planes better by putting more armor to where they observed bullet holes after missions. That didn’t help; as many planes were downed as before. Then someone suggested better cover for the areas they never saw holes in, and bingo! More planes started to return from missions.
Because those places were the ones, when hit, downed the whole plane, and they never returned. The holes they actually saw at the base were in fact relatively harmless, and those areas did not need extra help.
Similarly, you cannot deduce what makes people leave by observing those who stay. Those with more pvp experience tend to stay longer - but that can very well be simply because the game downs everyone not interested in pvp from the get-go. It does follow, if that is the case, that you can increase retaining rates by forcing pvp on uninterested parties.