I was also that kid, and now I use computer hardware and software skills daily in a professional capacity. Don’t get me wrong, I certainly agree with you on all points.
I don’t know what reasonable justification there is for doing this for consumer devices generally, from the owner’s perspective. Maybe it makes devices more appealing in a corporate context, for the same reason some secure environments forbid devices with cameras or recording hardware, and also forbid (re-)recordable media. Maybe it reduces loss in the supply chain for the companies to do so. Some credit card payment terminals have tamper-evident designs built-in prevent or deter dumping hardware encryption/decryption keys, firmware, and other kinds of tampering, to reduce fraud and unauthorized access, for the owner’s sake and the networks’ sake. I would like to hear some more or better reasons if anyone has insights into these topics.
That's a clear strawman though, unauthorized in this context clearly meant 'not authorized by the manufacturer', it's not the parents that install safety screws to keep the kids out, it's the manufacturers that do it to keep the owners out.