Nowadays hackers are highly smart. When they can enter into highly protected official sites of the governments and it is a matter of money they seek a chance to hack accounts. This is why it is advised to keep on changing the password after some time. Your password should be too complicated for hackers to get the password compromised. It might be possible that it is the rule of the site to keep it changing or any hacker is closer to hack your password and the site is realising that your password might be compromised in future if your password is not complicated. Moreover, one important thing I would like to tell you that when you intend to change your password, then type it first on notepad or clipboard somewhere and copy and paste it on the site. It often happens when someone takes more time changing a password online, hackers fund it easy to hack the account.