This is very interesting, although maybe something else should be considered: scrum masters as servant leaders are people too. They also have frustrations. And when the organization is a monster that at some point in time blocks every bit of the path for them to keep believing in being servant leaders... or maybe made of people who do this blocking for whatever reason...
Well... depending on a huge amount of factors, people that used to be servant leaders may very well give in to frustration.
Should they have done something like maybe look for new jobs before this happened?
Sure, but they believed they could change the world, so they took second and maybe third or more chances to make the change.
It is not always black or white.
But I do agree with one thing: if the scrum master already starts doing his/her work not believing in being a servant leader, they might as well not start at all.