The average person dont like linux, and if they buy a linux laptop the reason is because its cheaper than the windows one. So why manufacturers still use unknown distros (like lenovo with endlessos) and not something like ubuntu or mint?
If it's based on Debian then 90% of guides online will work with it anyway
Most of the Laptops I see with Linux are Ubuntu, some Ubuntu based distro like Tuxedo, Pop_OS, or Linux mint, and very Rarely Fedora (I'm not sure, but I think I saw one ship with Fedora).
Ubuntu is highly commercialized and trademarked so vendors that offer it make deals with canonical. Dell, Lenovo, and System76 have all offered Ubuntu in the past.
One thing that vendors do sometimes is they offer an official image that includes drivers for that particular laptop and they never make it into mainline. I think that's part of the draw for offering your own weird OS - you basically get to control hardware support and your own release cycle.
Control has other benefits as well. You get to do some branding, which bean counters love, so you get to deliver "the Lenovo experience" or whatever. I think System76 actually cared about this for good reasons and that's why Pop!OS (terrible name) is actually pretty good. Ubuntu kept screwing up their offering so they just did their own thing instead.
I know that some manufacturers ship QubesOS, those are intended for people with high threat models afaik.
