Availability - ThinkPads are very popular in corporate environments and are generally replaced every 2-3 years. Although mostly Intel CPUs, there is a wide variety CPU+GPU available from lightweight to high performance.
Tough + well built + last forever
Easy to upgrade/repair. They’re very user-accessible and its simple to upgrade RAM or SSD/M.2 drives. Plus, because they are so popular in the corporate environment, replacement parts (from batteries to WiFi+Bluetooth chipsets to trckpads) are very available and cheap.
Well supported in most (if not all) linux distros. Graphics just work, trackpads just work, WiFi just works.
Cheap.
Sent from my ThinkPad T580 (with both an internal and removable battery, I get 10+ hours of battery life)