It's mostly a matter of emotions and ritual rather than rational logic. Year-end holidays are loaded with memories and habits - since childhood, you associate this time of year with a specific place, specific people, traditions that repeat themselves. Even if technically you could work from anywhere, your brain needs that anchor. It's not just "being with family," it's getting back to that specific context that mentally takes you back to a version of yourself.
And honestly, remote work doesn't really change the emotional problem - if you stay alone in your apartment working, you'll feel isolated during the holidays. People really want to disconnect from everyday life and share something, even if it creates massive traffic jams. It's not super logical, agreed, but human traditions rarely are. There's also social inertia - everyone does it, so you do it, and that reinforces the cycle.
The whole thing with miles of traffic jams is clearly awful, but for a lot of people it's worth it. That said, some people are starting to change their approach - visiting family at other times, or negotiating to celebrate where they are. It takes a while before mentalities really shift on traditions.