Nothing, and so they do. Dell will sell you an XPS 13 with Ubuntu installed. Lenovo will let you select Ubuntu or fedora in some models. System76 and Tuxedo will sell you a bunch of laptops only with Linux. Starlabs sells Linux laptops. KDE sells a laptop. Purism sells Linux laptops.
Without accurate polling with statistically significant sample sizes it's hard to tell what the whole of the unions members think of the situation. Do you have some sources for this statement?
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