But paid Tailscale is $5 a month right? So you gotta be paying more to self host and deal with all the problems yourself, not have derp servers all over the world, etc. Why?

If you run multiple services it gets cheaper. I would not see a reason to pay for 3 different cloud services that I am able to self host.

Why do you assume OP paid $5 a month? You get Tailscale for free in many use-cases. Your argument that self-hosting is more expensive is still valid, but I don't get the 5$.

tl;dr: because I can.

I already run a VPS for other things, this fits cleanly into that setup, NetBird’s been low-maintenance, and I don’t need global relays. That’s enough for me.