I mean if you buy a surface book you get windows 10 pro installed and activated, so they’re kinda already doing this
This may be true for Surface Book- an uber-high-end device. But almost any other Surface device you buy through consumer channels has "Windows 10 Home" edition on it. If you want to use it for business to join a domain, you still have to pay the $100 "Microsoft Tax" to upgrade the edition to Pro. The last 20+ Surface devices I've purchased were all this way.
You've been ordering the wrong SKU then, look for "Surface Go 2 for Business" as an example (the lowest end Surface) and it comes with Pro for less than the cost of upgrading from the Home version.
If you're a Microsoft partner or resell there are also options available for ordering for use with Enterprise volume licensing.