They probably figure that if the fuse blows, it's because there is a fault in the device. There would be no point in replacing the fuse without first troubleshooting the problem and fixing it. ‡‡
With many devices "containing no user-serviceable parts" and the cost of repairmen being prohibitive, it becomes another disposable consumer product, cheaper to replace than repair.
Should the fuse blow when replaced, consumers may try a higher current fuse, or even a paperclip, so making the fuse non-accessible could be construed as another level of protection (of the consumer from himself).