Hosting, marketing, other promotional stuff (conferences, maybe other?), there are still three people on the payroll and otherwise I don't know (which was part of my point) as I've never run a business like this before myself. Oh, subscriptions to AI services... that's pricey I hear ;)
Hosting for their documentation would only be a noteworthy amount if they chose to host on Vercel. Other than that it's a Hetzner box at $100 per month tops.