1. Even if one loves macOS, Apple doesn't support its hardware forever. Being able to run an alternative operating system on unsupported hardware helps extends that device's useful life. My 2013 Mac Pro is now unsupported, but I could install Linux on it and thus run up-to-date software.

2. Some people want to use Apple's impressive ARM hardware, but their needs require an alternative operating system.

It is an inspirational demonstration of the hacker spirit and a way for the individuals involved to both expand their technical abilities and demonstrate them to prospective employers.

I personally consider it very inspirational though I recognize that I will probably never be able to undertake such a difficult task. I can imagine that it is very inspirational to the next generation of extremely proficient and dedicated teens who want to master software development and explore leading edge hardware.

if you want an arm laptop with incredible specs, incredible build quality, incredible battery life and incredible performance that runs linux what other option is there?

Some people really like the hardware but can't stand the software, and have the skills to do something about it.

macOS sucks. It does a disservice to the greatest laptop hardware package ever made.

To run Linux on MBPs

It's fun :)