Again: because you only have one player's name to memorize every 4 years! Whereas with WTF you start confusing years with players who won because it's held 4 times more often. Not difficult to understand.
Ofcourse it's a factor, but that doesn't automatically mean it's the only reason.
Slams are also held 4 times more often than the WTF, but no one mixes them up (okay, easier because of different ones, but still). If the WTF was really that much more important as some on here suggest, it really shouldn't matter.
The olympics are talked about way more often, it's been four years and I bet everyone remembers that smash Novak missed. If that was in a WTF semifinal, it wouldn't be remembered as clearly, even months/weeks after.