Windows 8.1 Pro won't upgrade to Windows 10 Pro?

I have Windows 8.1 Pro installed and activated (of course with a legit key) and I want to upgrade to Windows 10 Pro.

Everywhere I read about the upgrade it says I'm suppose to get the Pro version of Windows 10 because I got the Pro version of Windows 8.1. But this doesn't happen, but instead I get the Home version. Why?

I'm upgrading from Microsoft's web page.