Sometimes, it seems, Microsoft will actually OEM Windows at a loss. A year ago I bought some NUCs with Windows pre-installed that were less expensive that if they came with Ubuntu. Microsoft apparently felt is was important to try and hang onto that market. I bought the less expensive NUCs with Windows and then formatted them and installed Ubuntu, saving myself around $40 per machine.
I think the reason for the this is the additional software applications pre-installed on top of windows where the publishers of those applications are paying for the right to be “distributed” in this way. Think in terms of software that is pre-installed but requires a subscription for continued use like anti-virus software, productivity software, media editors and players, etc.
Ie: the Windows OEM license costs less than the total amount of money that the other software publishers are paying for distribution and if you reject windows, your are rejecting things that subsidize the price of the PC itself.