Size doesn't always mean clever.
I just plugged an HDMI cable into my TV all by myself, it shifts more than 7Billion bytes/SEC to the screen.
They're not just doing redirects, they're doing a lot of data science with exploring the statistics of what gets shared, clicked, etc.
Same for spam filtering, automatic reporting using the "+" links etc. At some scale level keeping up any service becomes a nontrivial task.