I don't have to do this on my laptop. I have 10 and 15 year old laptops that I can run the latest version of Linux straight from kernel.org on for free.
The Android running on your phone is not FOSS. If someone wants to write free software that runs on your phone they totally can (and do, check out Graphene).
To an extend yes but it's unnecessarily hard to do so. If we were at a point where is was as easy to develop foss OS/Software for mobile devices I wouldn't complain. Sadly the proprietary nature of mobile phones (mostly drivers) doesn't allow that.