For the same reason people wait for midnight on new year.

It's an arbitrary thing people do for fun.

it's like any holyday, it's a rendezvous for the community that recognizes it. it strengthens the social bonds

You got downvoted for this question but it’s such a great question in this context because like the UNIX epoch, the answer is arbitrary :)

Incidentally, I guess the windows/NT epoch started in 1601.