I'll throw my 2 cents in as someone who bought a 435 ES a few months back.
First off, I work mostly in commercials. I'm lucky enough to have made a point of fighting to shoot film on most of my projects and its largely a part of my work. Last year my work was more than 50% film, something I definitely don't take for granted.
Shooting on film isn't financially a smart decision but bringing film onto a project changes the dynamic as you know. For me, owning the camera was more of a move to help sell shooting film on lower budget projects that are already considering shooting film. Most of which are music videos or commercials, which you'll only be running a few rolls.
I also have an Arri service center 20 minutes from my house which played a large part into being open to buying the camera.
I can't speak to why so many are popping up for sale. What I can say is a great tool and I have really enjoyed working with it.