I totally understand why you'd rather be spending time in sweats relaxing with family. I suppose it could be a matter of what one is looking for. It's gotten boring just waiting for the ball drop on TV. So much so, I was in bed when 2014 arrived.
One of the few trips I made to WDW was to ring in 1990. Day One of our visit, if you can call it a "day," was simply to ring in the new year at the Magic Kingdom with the throng of people. We strolled into MK fairly late at night. No rides planned, just the fireworks. It was kinda neat to celebrate the new year among a crowd for a change, instead of with a few select people.
As fun as it was, hearing kids all over the place blowing noisemakers for a couple of hours was incredibly annoying. And there was a cloudcover that obscured the fireworks. Still, it was a pleasant, memorable event.
The next few days that we were there, the crowds were relatively thin, and the trip was enjoyable.
So to sum up, someone might want to be among many thousands of people to celebrate the New Year with a midnight firework show. That's why they might be there. But I'll agree, making it a planned park day would not be wise. I'd rather be relaxing in MY sweats somewhere.