Docker Engine (which is the core of what people think of as “Docker”) is FOSS. Docker Desktop (which most people rely on for local development) is free for individuals but I believe the license says companies over a certain size are required to pay.
And on top of that the paid plans also come with support, which large businesses frequently require, and private repositories on docker’s image repository.
I think docker desktop’s bigger value prop is that it’s a well supported zero-effort setup of a VM to run the docker daemon on platforms that don’t support it natively (i.e. MacOS which a lot of programmers use). And it very cleanly handles mounting your local filesystem into containers running in the VM, which is important for dev envs and used to be a source of friction with alternatives (although it seems like the competition has caught up and this also now works out of the box with rancher desktop and others?). Having a GUI is somewhere behind those, though I know folks who have a weird preference for GUIs 🤷♀️.
I’m just a guy who uses Linux and spends most of his time in a terminal, so I’m not saying I value docker desktop, and I personally don’t have to deal with any of this so I’m probably behind on how good the alternatives are. Just saying where I see other people get use out of it.