system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can a seemingly simple app, like Pandora Radio for example, employ thousands of people and keep them busy for 40+ hours per week?

I know there's a fair amount of programming involved in the initial development and updates, but it seems like there wouldn't be that much to do. What am I missing?
gpt
Unlike any other streaming music service, Pandora has actual people listen to every song in their catalog, multiple times, to identify the attributes that allow the system to select music for the listener. Other streaming services use software to do this, or use algorithms that rely on similar artists or other listeners' song lists. 

The other big part of any business that lives on advertising revenue is the marketing department - which is not marketing to users, but rather to the advertisers that provide revenue (subscriptions are a very small part of their overall revenue). Pandora's customers are the advertisers, and they need salespeople and other staff to service those customers.