I like the premise of having a Scrum Master serve multiple teams for this reason, but in my experience many organizations use this approach because they don’t see the importance of the role (for example like the first two points I mention in this story https://medium.com/serious-scrum/the-not-really-scrum-master-job-description-3b0750fd8006 ).

They assume being a Scrum Master is a job that anyone can do for a couple of hours per day...tops. But then, they want to keep this “resource” utilized at full capacity to justify a full-time employment contract, and if the Scrum Master can’t be something else also (like being a developer, BA, DevOps, etc) then they should cater to other teams’ needs too. Scrum Masters then spread themselves too thin and the Scrum implementation suffers in many - if not all - Scrum teams in the company.