Hanukkah starts at sunset on the 20th.

[Yelnoc]

It's not even the most important Jewish holiday.

Beyond that; it's one of the least important.

It seems kind of odd for one of the least important Jewish holidays to coincide with one of Christianity's most important holidays (second only to Easter).  I guess that's on purpose so as to not overshadow or short-circuit the importance of Christmas.

Uh, our holiday is way older than yours, unless you're counting the pagan roots of Christmas, which is the only reason you celebrate on Dec 25 anyway. And Jews don't take Christianity into account when we're scheduling our holidays.

It's only about a century and a half older than the birth of Jesus, IIRC.  Which might sound like a lot, but historiographically speaking, it's not.  And as you point out, the Winter Solstice was celebrated by Germanic tribes centuries before the Jews began Hanukkah.