In my experience (and I think also in the spirit of the analogy), it's not just maintenance. It's expecting to maintain everything you've ever done while also simultaneously being expected to keep producing new work at the same rate (and then being expected to maintain that).
It's that your work load seems to only increase. As the study found with regards to the causes of burnout, increased workload cited as the main reason.
I'm still providing updates to stuff from over five years ago (that has officially been retired), while my boss is breathing down my neck about new projects. The stress of doing this, the stress of trying to manage my manager's expectation, the stress of realizing you'll never be able to really put any of your work out of your mind or have a lighter load of responsibilities, etc. is what leads to burnout.