Usually when an engineer asks this question, they are starting with the assumption that most everyone who works there is an engineer. That assumption is usually wrong.
I have no inside information at all, but my guess is that engineers make up less than 1/3 of the employees. I'm sure the sales team is large, the product team is large, and the community management team is large. They probably also have a bunch of legal, and we know they have a lobbying group as well. And of course if you're taking people's money, you need a bunch of customer service to handle that.
When I worked there 14 years ago, we had at peak six engineers, and three non-engineers (one sales, one product, one community). But also we had the parent company providing legal (and there was a lot of legal requests even back then!), HR, facilities, finance, and basically all the other support tasks. And also we the engineers did a lot of it. We managed customer service for ads, we managed making t-shirts and plushies, we managed customer service for reddit gold payments, and a bunch of other "non-engineering" tasks.
The site is big and is transactional, which makes it a harder problem to solve. With the near-real-time display of votes and listing changes and comments, it's a lot more like eBay than Slashdot (which is what I would say at the time).