Maybe they are also in the wrong if the telemetry is excessive, but the alternative is to never deprecate any feature ever.
Better than keep removing features and reasons to use Firefox from some of their loyalest users, even if they are a minority. User retention seems Mozilla's largest issue at the moment now they're down under 10%.
Also, 0.01% of a big number is still a big number, and given the state of the feature, that number is likely to include a lot of long-time users.
When resources are constrained you have to make decisions about what features you'll continue to develop and which to cut out. Live bookmarks was cut out. Mozilla devs have also mentioned that this feature is ancient code and would have required a lot of coding effort to bring up to date.
I'm sure if you were to invest the time to reimplement live bookmarks with modern code and with the internal restructuring in the browser in mind and you'd volunteer to maintain it and fix all filed bugs, they'd accept it.
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.