There was a database leak in 2015. My guess is most of these hacks are related to this database leak.
Most of the accounts are registered after 2015
You can also take consideration of the phishing sites. When you look for bitcoinTalk on google, it pulls up few phishing sites who wants the credentials of your bitcoinTalk account. So phishing sites are another way of getting hacks.
No, frequent users do not use google to connect to the forum. Either they type the URL address or they use the bookmarked URL in their browser
a bitcoinTalk account with a good rank worth good money.
There are more accounts hacked with a low rank than a hight one
main reason of account hacks is phishing websites and people using weak passwords.
I hardly believe the number of people using a weak password is so hight