How come my iPhone 5s just quit vibrating even though it's still turned on?

[iMore Question]

In my settings I have my 5s set to vibrate however it does not vibrate for anything

 

[Tartarus]

Could be a mechanical issue. As with everything, nothing lasts forever.
Make an appointment with the Genius Bar at the nearest AppleStore or with a certified Apple repair service to have it looked at.