Historically because it was impossible to have everyone vote on everything all the time. Nowadays you still have the problem in some sense due to trust in voti

Historically because it was impossible to have everyone vote on everything all the time. Nowadays you still have the problem in some sense due to trust in voting systems, but theoretically you could run many of the functions of congress via calling a vote to the general population and they could do it on their smart phone or something. Auth would be hard(ish) from a practical perspective. Knowing enough about a topic could be easily resolved via allowing voters to appoint a proxy on certain bills or writ large.