The problem is that Linux and it's ecosystem are completely fragmented. Say that you deliver the laptop with your own Linux distribution. People still expect that you support dozens of other distributions, desktop environments, etc. Providing support will probably blow away the relatively thin margins that most manufacturers have to work with.
The only company well-positioned to take marketshare from macOS is Windows. They are doing extremely nice work with Windows Subsystem for Linux, which is quickly moving closer towards providing enough of Linux to be productive. At the same time, Windows provides good driver support for recent hardware, applications such as the Adobe Suit, etc.
Unfortunately Microsoft has to screw up with telemetry, etc.