Though, maybe it's not doing business in the US, and maybe the app is not similarly geo-blocked.
Actually can you not just pull the app and then side-load it anyway? That's what I would do if I couldn't get Tailscale from the Play Store...
Maybe this comment helps shed light on who I think are real the cause of your ire. Frankly I strongly agree with Brad's comment on why they don't care to open source the iOS client like they do the Android one.