Why haven't any link aggregator sites tried automating the voting system? Take something like view time and commenting/opening the article as a vote and perhap

Why haven't any link aggregator sites tried automating the voting system? Take something like view time and commenting/opening the article as a vote and perhaps still have a flag function to help remove off topic or illegal content. Manual voting seems like such a ham-fisted approach at finding what people want, and it disproportionately rewards those who vote over more passive observers.