Also the numbers just don't add up for large servers. The average server on here has about 500-1000 people. Let's say 1000.
Even if they had just one moderator, that's a ratio of 1:1000 staff per user.
Twitter has about 300 million users, so to get a ratio of 1:1000 they would need to employ 300,000 moderators. Depening on who you ask, the actual number of total staff at Twitter is 2000 to 7000, and only a small fraction will be moderators. That's why they use algo.