The easy answer is that the system for presidential elections is part of the constitution, and is quite hard to change, on purpose. You should know this if you'

The easy answer is that the system for presidential elections is part of the constitution, and is quite hard to change, on purpose. You should know this if you've graduated high school (since you live in the US). The second reason is that it is not clear that a "secure, nation-wide popular vote counting system based on modern communications technology" is a good idea even before we get to the technology. Our system of government is a type of federalism (state/national) and moving to a popular vote based electoral system weakens this division. I don't have much expertise here, but can assert with confidence that expert opinion is divided on whether or not this is desirable.