When they said Reddit has 2000 employees I was shocked. what could they possibly do onto a website that is basically run by users (and sysadmins) and that is basically feature-wise mature? I really can’t figure out 2000 people working every day on Reddit… on what? just for a quick comparison, the whole IAmA was run by a single person (Victoria), so… what are they doing?
I don't know anything about working at reddit, but I've worked at enough software companies to know generally what people do all day
HR - hires employees, deals with insurance and other perks, fires employees, probably communicates with the board or governing body.
Software - there are a few departments here, the most interesting of which is programming new features. Most will never see the light of day, but they're working on them.
QA - tests new features and bug fixes and patches before they go live.
IT department for when developers computers do unexpected things.
Tickets - a team of developers/systems engineers to fix bugs and issues in the production source code. They will typically have 1-10 people on call at all times outside of normal business hours.
Systems Engineering - they decide how and what systems to implement, upgrade, retire etc. They need to coordinate with developers to plan software/hardware upgrades to make sure they don't mess anything up unexpectedly (but it almost always happens during an upgrade)
Accounting - Accounts Payable (when you pay money for something, like AWS); Accounts Receivable (when you receive money, like for artificially inflating posts to the front page for money); Finance - should and how much money should be borrowed/invested to run the business; and a ton more depts honestly, any of which without the business would crumble.
Advertising - Both advertising Reddit in other media, and arranging sponsors to put their ads all over the place.
Executives - they plan the strategy for each dept listed above. Although this being an internet service, the CIO might be slightly more inflated than a typical company.
And there's probably a lot that I'm forgetting. But really, all this is just to illustrate about one of the most trafficked websites every is "How are they running a business with only 2,000 employees"
100% agree, here's some more departments that you haven't listed but probably exist:
Legal, internal contracts, contracts with suppliers, contracts with customers (advertisers), compliance with the laws of many countries/markets
Regulatory, compliance with internal and external regulations
Procurement, negotiating with suppliers
sustainability, there's probably someone in the business reporting on gender balance and environmental impact and a host of other UN SDG considerations
PMO, internal project management and portfolio reporting
market X, there may be a team of people for each major market responsible for sales, infrastructure, compliance, etc. in that market, in addition to central
CI/productivity, there will be some team responsible for reducing costs
Product owners, there will be teams of people responsible for arguing about what features/bugs should be implemented/fixed
monetization, there's probably dedicated teams looking at (and a/b testing!) new ways to push people into spending money on the app and/or interacting with ads more often