I'm fairly sure that was because of laziness at Microsoft: they only wanted the most popular games to work so people would be more willing to upgrade to a 360. Once they'd got those working they made a list of what was fully compatible, so you can't boot anything with a bug, no matter how small. That's my understanding from research I did 8 months ago, so I may have misremembered something.
OS: Windows 10 64 bit Professional
CPU: AMD Ryzen 5900X
RAM: 16GB
GPU: Radeon Vega 56
CPU: AMD Ryzen 5900X
RAM: 16GB
GPU: Radeon Vega 56
