How do they actual make money? I've been using Resolve for years without paying for it (and without thinking about its business model too much). It seems that they sell quite expensive professional hardware so I assume the software users are just compensated by hardware users?
Hardware. It's like the Apple model (before they got into services). They sell a full suite of hardware that works great with their software, and they see the software as a way to keep good will, and also showcase their tech well. They also sell a paid version, if you want a few extra features.
Also they were first to sell us USB3 based HDMI capture devices that we could take around and do live capture from cameras at full HD for also a pretty affordable price (around 1000$?).
Whenever we needed affordable (semi) professional gear, they were consistently the ones to look at.