That's like saying that you insist on using the Windows XP image that came with your laptop forever and will only update through the vendor rather than just installing the latest Ubuntu image.
We really need to stop giving a fuck about manufacturer images and demand that the industry ceases to lock bootloaders so we don't have to wait on them to update anything.
Unlocked bootloaders everywhere would be nice but there are already manufacturers that give you that across the range. The big issue is that none of the drivers are upstream so even with LineageOS you're stuck on and old and often unpatched kernel. When a new Android version comes around it's common for support to be dropped for devices. Right now there's no Ubuntu-like experience with Android. Get a Pixel or an Android One phone if you care at all about security and access to new Android versions.
No, it's like saying I want to get Windows Updates from Microsoft and not some random person on a forum. It would be great if Google published a full Android release that worked on all phones and had the manufacturer's best experience in mind, but they don't. So the next closest thing, the company I choose to put my trust in, is the maker of the phone. The company who originally installed the OS in the first place.
I want updates from a company who can be held accountable. Not some random ROM from XDA.
We really need to stop giving a fuck about manufacturer images and demand that the industry ceases to lock bootloaders so we don't have to wait on them to update anything.