- MacBooks are still among the nicest if not the nicest laptops hardware-wise, so some people like to run Linux on it.
- People have older Macs that they like to repurpose. E.g., we still have an M1 Mini that was used by our daughter before she got handed down a MacBook from my wife. It's now collecting dust, but I might install Linux to use it as a headless server.
Also, this is Hacker News.
By the time said macbook is fully supported, it is in sorry state. Judging by what I found when looking for second hand laptops, macbooks don't age well.
Are you dumpster diving for your MacBooks, perchance? I buy all of mine second hand, they are all still mint by the 5 year mark, and I have several at the 10 year mark that all I've had to replace is the battery.
The problem with used Macs is that they're still really expensive, and if you want to only run them with Apple software, the support duration is limited (especially true for phones, even more for Android ones). You can pick up used Thinkpads or Dells in great condition for very cheap after a few years.