Very large numbers of relatively weak demons are more reliable than small numbers of very powerful demons. Interaction between the demons should also be strictly controlled and regulated with demons operating in relative isolation most of the time. An errant or exploding demon in rigid confinement causes less damage than one blows up as it travels freely through the system. This is the difference between Linux and Windows and is the reason why Linux is so much more stable. Of course, this philosophy can only give us computers that are highly reliable, but still not infallable.
Nothing is perfect.
Ask your physics professor. The reason is very simple. Magic wields much more power per unit of force than does Science. As an example, no oven can heat your food in 30 seconds without scortching it. Also, early computing devices that worked wholly on Science such as adding machines and vacuum tube computers consumed enormous amounts of power and physical space and were slow in speed and had to be virtually rewired for each specific task.