Well, it is not exactly like that.
As far as "being a cellphone" or behaving like one is concerned it is not the authorities or nations or whatever that dictate that a device needs to be trackable and traceable, it is the nature of the cell network.

If a device needs to be able to connect to some provider network, be it of the GSM family (GSM, WCDMA, LT, 5G) or some CDMA-2000 derivative the device needs to register to a cell in the network with a persistent identity to be able to send and receive anything. This is a technical requirement and not a political choice; there also exists an open-source stack for 2G GSM communication and nothing prevents an able hacker to code an implementation for more advanced RANs.
TLDR; You can have open-source baseband implementation if you want to.

On the other hand the network was built this way for a reason, to be able to target billing correctly to the users and segment different services and service levels to paying customers.

If someone codes an open-source 5G baseband it has to operate by same rules as the closed-source implementations, or else the signalling just does not work; the TE needs to register to a cell with known identity or there is no communicetion. Period.

If there would have been a will to create an other kind of network that would enable anonymous and location-unaware communication between TE's, then the network would need to be designed differently. These design choices of the existing networks might well have been partly influenced by government agenda however more likely is that it was implemented the way it is done because that is simple and cost-efficient.