Given how long ago it is since live bookmarks were a feature they made obvious, or called attention to in any way, in the default install, that's not so surprising.

They removed the visibility years ago, then progressive updates made them ever less visible, including hiding then removing RSS notification. Once the first step was taken, the route to removal was set, including the telemetry figures.

If they were as visible as pocket, perhaps as visible as pocket stories on new tabs, usage would be hugely higher.