You talk about Apple but Apple is not an excuse because they are bad themselves, yes Apple also sucks.
Do you really think a normal user will be able to unlock or install Marshmallow on his phone with these unnecessary complex instructions? I have rooted and installed a few Android mods myself and I can tell you that it is very easy to make a small mistake or that the third party instructions are not clear enough so you end up with a bricked phone. I am not talking about myself, you or other technical people. My sister, mom or my grandma will not be able to install this crap.
If the company can't support a highly expensive device for more than 2 years then the install process should be as simple as dowloading a Google app that will update the phone. This is something that Google could easily do if they would just get of their asses and stop being evil.