As I understand it, most enterprises have an agreement with Microsoft for commercial licensing of Windows that lets them pay per user instead of per machine. Given that most enterprises tend to lock in a contract with their hardware provider of choice, it wouldn’t surprise me if they had something in there to omit Windows since they already pay for it directly. Plus enterprises windows has features for managing windows at scale (group policy, centralized auth, etc).

I worked for one of the IT departments at my university and we got Ubuntu machines straight from Dell on occasion. I recall those machines being somewhat quirky if we tried to flash them with Windows later (might have been missing a TPM header, or equally arbitrary hardware requirement, but it’s been like 10 years).

In the consumer space, Framework will also let you skip buying a windows licence as well.