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.
Did you just assume no one sells a Linux laptop?
Yes, I support providing free school lunches to both rich and poor students. It removes the stigma of receiving free or reduced cost lunches.