In the early 2010s one of the biggest issues with smartphones was battery life. The packaging of the battery is limited if a requirement is to make it removable (i.e. it must be a certain shape, have connectors in a certain location, etc). If that requirement is removed, battery can be made to fill whatever space is available in the device.
People drop their phones in water all the time. Then call the company and complain it's broken. People get mad when the company tells them it's their fault. If you have fewer holes in a device, it's less likely to be damaged by water. A removable battery means exposed connectors sealed by imperfect covers, making them more likely to be damaged by any water ingress. So they removed that failure point.
Another issue in tech generally is end-users messing with the device internals, accidentally breaking the device, and blaming the company. Remove that failure-case by making the internals inaccessible and complaints go down.
Making the device impossible to access because of a deep-state conspiracy is just a convenient mental shortcut to believe in. I'm as annoyed as the next person about less-repairable devices but I don't think it's a conspiracy, just practical engineering.