Pretty sure you need a lot of reports in a short period of time to get a ban. Im not sure how many reports are needed but if im not mistaken it needs to be reports made across a number of games which is why it takes time even for blatant aimbots to get banned.
If the system is not automated would mean a person to review all the reports made by millions of players and i imagine then nothing will ever get resolved. Both the guilty and the innocent would run rampant.