I'm not sure that I think that burnout is directly related to a job being fulfilling. It seems to me that it is more related to having a lot of responsibility but very little power. Or somewhat equivalently, being in a position where other people can make your work much more difficult without you having much control over it.

In software at least, I think it could also be related to the pace of modern development. Agile sprints mean that you are constantly in a situation where things are down to the wire.