How do people hack e-mail accounts?
Leveraging the fact that people who own the hacked accounts are reckless, irresponsible and/or don't care and/or don't have a clue about the minimal set of steps to protect their online credentials, e-mail account included but not limited to; (Quora, Facebook, Google, Twitter and many other accounts included as well).
People also fall, out of ignorance or excessive confidence, victims of social engineering schemes where they inadvertently reveal information that eventually conducts the cyber-crooks to conquest their target accounts. This includes writing their id and password in post-it like papers, having extremely obvious passwords, using email and other online services in public unsafe computers, leaving their sessions open while absent from their computers, using same password everywhere... and the list goes on and on...
You name it, ignorance and recklessness are the main ones to blame...)