ThinkPads are business machines and those are extremely repairable compared to consumer machines. Even my shitty Dell precision has instructions on how to disassemble it etched onto the mainboard. And since business laptops get dumped after a few years of relatively light use (many are de facto stationary), you can get pretty good machines for very cheap.
ThinkPads are just very popular, because they are consistently pretty good and don’t stand in your way softwarewise, which isn’t always true for Dell or HP machines.