Better security, DirectX12, full support and feature updates, lower system resource use than Windows Vista through 8.1(not by much, but it's there).
Honestly, the privacy thing isn't a big deal - most of the telemetry Windows is sending is for diagnostic purposes so they can fix potential issues before they happen and better support the OS. The other stuff is sent for advertising purposes, which, if you own any google device, you're already sending to a major corporation - no big difference there.
You can disable all that stuff, too, if you really want to.
I'd typically recommend Windows 10 Enterprise LTSB N edition for the very paranoid, but it's only available through a Volume Licensing agreement with Microsoft.
Compelling reasons why you should not? well, the start menu in Windows 10 is atrocious. Otherwise, I think most things are pretty much the same as 8. If you hate the Start menu like I do, use one of the following:
StartIsBack (My personal choice and favorite)
Classic Shell
Start10