[RockRobotRock]

I really thought Tailscale would automagically figure this out. If this were true in all cases, my internet would not work at all since it would try to reach my router through the Tailscale interface.

It's odd.

[windexh8er]

The SR can't route for your gateway or else Tailscale itself would break it's own connection. A gateway IP isn't treated the same as a subnet route.

[readyplayeremma]

You don’t have any specific routes to random internet addresses though. And Tailscale would not either. Unless your Windows server is running BGP, all your Internet traffic is hitting the default route.