Comment by m4rtink

Consumers decided - and Google also decided to ban manufacturers from building phones with another OS or they loose access to Google Play store and Google apps on the lucrative Android phones they also manufacture: https://arstechnica.com/gadgets/2018/07/googles-iron-grip-on...

(the article is from 2013 but was updated in 2018)

So no manufacturer that already builds Android phones will make an alternative OS phone for you - and that's effectively all of the mobile phone manufacturers given Apple makes all of the iOS devices.