Two reasons for me
1) The COVID-19 lockdown has given me a lot of spare time for projects, and I wanted to see if I could get an old bit of junk I would have normally thrown in the skip working with MacOS. It takes me back to the days of early Linux hacking, and the scenarios are similar - you needed to watch your hardware, understand what the kernel did and how to write config files and read logs. Back then you needed to avoid Diamond video cards like the plague because they had no open source drivers, and to get any sort of GUI, you needed to manually configure an XF86config file with the horizontal and vertical modes from your monitor's manual.
2) I have a love-hate relationship with Apple. I like their software; specifically no audio app can touch Logic Pro X and the Hammond organ sound is better than my Nord Stage 2 keyboard that cost £2,500 (and you think Macs are expensive!), and I just feel more comfortable working on Macs than PCs. However, I utterly detest the proprietary lock-in technology that makes something simple like putting an SSD in a Mac Mini such an arduous process, and think their AppleCare policy of "throw the old equipment in the bin and charge the customer for a new unit" is draconian. Have a look at Louis Rossman's YouTube channel; he basically makes all the points I would, but better, and has scared me away from ever wanting anything to do with MacBooks. (One of my laptops runs Linux, the other runs FreeBSD).