I dunno who put together the field of 16 here, but it's hardly a evenly spread competition when it comes to release years. ROTK, Silence of the Lambs and Platoon as the newest entries? Please. Of course the label "of all time" should contain older films too, but primarily? No.
I simply do not subscribe to the POV that the best films of our time are older than the 1960s. That may be personal taste but the constant "back then everything was better, no special effects but real stories"-whining is a huge pet peeve of mine. Films dealing with themes from so many decades ago hardly ever touch me, their way of acting, writing and filming feels dated and wooden to me. Some of my all-time favorites are from the 70s, but none made this list.
Of course that doesn't mean people don't have the right to vote for Casablanca. But no one should be surprised that people pick a more recent film that represents film-making as it is done today, especially combined with a timeless story loved by readers for decades.