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.
Tramlines are a nightmare for cyclists - the tracks are just wide enough for a bike wheel to get jammed in them, and what happens next shouldn’t need any explanation. One of the professors in my undergrad met his maker that way, and it was part of my own education when first moving to the city as well. Beyond anecdotal evidence, the statistics are not pretty.
Of course there are good things to be said as well - I generally prefer the tram to buses, and especially when it has its own dedicated lane outside of traffic (ideally in a green area) it can be both a beautiful green space and a great alternative to cars. But if it has to share space with other traffic, which is usually the case, it comes at a cost that is greater than just the one of construction.
With good planning of infrastucture this is less of a problem. I say this as someone who’s suffered minor head injury and minor TBI because of the mentioned problem. Only reason for this was I was obeying the law in a place where the only legal place to cycle was in this case the most dangerous one too, and where I had cycled numerous times before without an incident. Now it luckily has a separate path for cyclists, and soon the tram tracks are located in a place where you’d have to do mad stunts to “get into the groove” (no pun intended).