It’s cheaper to make, less liability if something goes wrong on the user’s end, impossible to replace by user for he needs to go to the manufacturer, planned obselescence, many reasons.
Yeah. Apple, for example, makes it impossible to repair their devices yourself and charges a shit ton of money for repairs.
You're basically forced to keep paying them more money, or risk getting your warranty voided if you do it yourself or go to third party repairs.
It isn't always a surveillance thing. It's a business thing too, sometimes.
As /u/wallnut553 already mentioned, cost efficiency and reduced liability is the official reasons. However, the batteries are still exchangeable (be care full and follow the specs), some comes with a custom connector, others require a soldering kit.
I'm convinced that governments was pushing into this direction as well. This is big brothers main tool to keep track on the masses. It does not matter if you are at Manhattan or in some jungle or desert in Africa, mobile networks are almost everywhere.
You're basically forced to keep paying them more money, or risk getting your warranty voided if you do it yourself or go to third party repairs.
It isn't always a surveillance thing. It's a business thing too, sometimes.