And also as a small fish the higher OEM price is being subsidised by the Fortune 500 companies which buy millions of dollars worth of products from Dell etc.
Edit: The idea that OEMs only tack on the extra cost to big companies is demonstrably false. For one thing, margins per-item are always lower on bulk purchases, not higher—Fortune 500 do not pay list price on anything. For another, you can see the difference in cost on the Dell XPS 13 by switching between Linux and Windows:
https://www.dell.com/en-us/shop/dell-laptops/xps-13-plus-dev...
Computers that don't offer a Linux option just all come with that $149 surcharge baked in.
You get Windows for free from the combo of self-assemble + torrenting + Microsoft not pursuing individual users for piracy