The reason why its happening is that most people don't care and don't need that freedom.

Otherwise they wouldn't buy android devices, right? Thats how freemarket works.

Its much easier for people to give away their freedom to install any software on their device in exchange of not learning all the intricacies of information security and privacy.

EVerybody still can install non native os on their device and use any store they want, right? Or fork android and maintain the OS that allows installing software from other sources.

Its just people don't really care - google is not non profit - its doing business for people who pay money and care more about passing the security reaponsibility on the manufacturer, thats why Apple thrives and nobody cares that you have to use their store only, only minority of people who are not an interesting market