Money. It would be way too costly that all countries manufactured their own devices.
A single laptop has likely hundreds of processing units, running unknown software, often with direct access to the memory buss. Building a secure devices however where every bit of code and every bit of hardware is designed domestically (and preferable in house) is so prohibitively expensive that no one do that. The hope is that if there is a security fault then someone else will find it and report it, and so a reputation system is the only economical viable method for hardware security in most consumer devices.
A single laptop has likely hundreds of processing units, running unknown software, often with direct access to the memory buss. Building a secure devices however where every bit of code and every bit of hardware is designed domestically (and preferable in house) is so prohibitively expensive that no one do that. The hope is that if there is a security fault then someone else will find it and report it, and so a reputation system is the only economical viable method for hardware security in most consumer devices.