For me it's the data-hoovering. I don't want Samsung (or Google, or Xiaomi, or whoever) background services phoning home my location every few seconds, or being able to uniquely track my device across apps, etc.

Once my ability to run a "background spyware-less" Android device went away, so did my willingness to put up with the negative sides of the usability tradeoff.

Apple probably sends some telemetry home, but at least their business model doesn't depend on knowing the exact Pantone color of the food I ate for dinner to market a matching wall paint to me.

Edit to add: oh, yeah, you mentioning 3P apps complaining if they detected root or MicroG reminds me of many a horrible night of debugging. Ugh. What a mess.