Currently if you have disabled report types in your navigation such as List, Pivot, and Chart, they won't show up as option in the report type switcher. The toggle only shows up if you enable at least 2 of list, pivot, chart or roadmap reports.
With nav option enabled:
Without nav options enabled:
Sometimes admins want to keep the navigation cleaner, but they still want folks to have the ability to switch view types here.
Also, this isn't preventing access to a report type because users can go to Roadmaps > Overview and access/edit any report they'd like.