I can't imagine the supply chain challenges inherent to startup laptop manufacturers. I think it's "go with what you have access to at reasonable prices, or forget about it. "
EDIT. Actually it looks like I was wrong about that. They do apparently at least make their own chassis’s unsure about the motherboard’s or screens though.
System76 has long been working on their own laptop - every few years they make a progress report announcement - but I don't expect to see it anytime soon.