Question Why can't i install any OS i want on a phone, like i can on a PC

[master_andreas]

i have been looking to buy my first phone, and as someone who values highly internet privacy and anonymity i wanted to avoid the android OS, so i was looking at alternatives (ubuntu touch, manjaro) but a quick look at the compatibility list shows only a very small list of supported devices.
why is that the case?
can i install the OS anyway on any modern device like i can on a laptop?

from a top eye view i can not see any reason why it would not work, thanks

 

[Ravynmagi]

Unlike x86 PCs, my understanding is there isn't really any standardization on smartphones. Like with Ubuntu Touch, Lineage OS, or any other OS, there is a lot of work that has to go into it to make the OS compatible with each model of phone. Why it's like this, I'm not sure. Though I imagine Google and phone manufactures have no interest in making it easier to install a third party OS.