Even if you think what you would say is obvious, please add. This is genuinely something I think makes sense regarding local bus routes given the longevity of light rail and how infrequently routes change, but I also suffer from confirmation bias, so I’m hoping for reasons this would be a terrible idea but obviously would prefer reasons it would be an even more amazing idea than I thought.
Another problem with light rail would be mountains. Trains don’t like those. On the other hand, cable-cars and cog railway exists and seem to be viable solutions. The city of Lyon even has both and since the cog railway starts on a flat terrain, it is able to switch between both.