The date in a Copyright notice is the date of first Copyright for the works. You do not update it to the current year. However, some sites do suffix the current year as well (e.g. 2012-2016), although that's not required as it's already implied (by dint of displaying the notice in the first place).
Because not everybody knows even if they should. Because it makes things easier for others. Because it facilitates contacting you for licensing deals and you want this money. Because it makes infringements easier to prove since you haven't officially registered your copyright. Because you want to sign your work.
See -> https://en.wikipedia.org/wiki/Copyright_notice#Form_of_notic...