They do let their Windows DIY user fix problems, for example the new AMD laptop requires a modified ISO, since the Windows installer don't have up-to-date wifi drivers.

Also Windows user needs to use command prompt to install firmwares, whereas Linux users don't need to.

All of these are documented in detail in their guide: https://guides.frame.work/Guide/Windows+11+Installation+on+the+Framework+Laptop+DIY+Edition/116

So I don't think they prefer Windows than Linux. It is just the nature of cutting-edge hardware: I believe they made the tradeoff between cutting-edge and stability (keep in mind, you can buy older hardware as well), not between Windows and Linux.

The only thing they can do better is have laptop preloaded with linux, but I cn kind of understand keeping laptop in stock with three different OS's and a DIY version while keeping everything up-to-date is a logistic challenge. Yet several linux laptop manufacture do offer that option.