Computers are more or less the sum of their parts.
For the longest time, and even now I think, the “Linux laptop” companies mostly sold re-branded quasi-generic laptops from Chinese manufacturers and focused on the software aspect to ensure compatibility. This meant that a lot of aspects were cheapened out on. The chassis, trackpad, keyboard, display, fit and finish in general were second class. Sure it was a machine that ran Linux, but most computers do that pretty well.
Laptop shopping is already fraught with pain and hazards. How do you know you’re getting something that wont break down? Add the “vote with your wallet” premium price on these boutique Linux laptops, and they don’t seem that appealing.
Thinkpads on the other hand have a huge community of nerds documenting compatibility. They have enterprise customers dumping pallets of used machines into the used market every year, and have far better parts accessibility than the quasi-generic machine.
Then there’s the trackpoint, you never need to leave the home row. You’re not victim to subpar trackpads(Every non-mac trackpad is subpar, sorry, I don’t make the rules, they suck absolutely.)
I’ve had my X1 Carbon 4th gen since new in 2016. Even if I can’t upgrade it, 7 years on its still nearly perfect. I got an Dell XPS 15 from work ~5 years ago and I’ve gone through two batteries, finishes are wearing off, the hinge is wonky, and IT HAS NO TRACK POINT.