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.
Light rail is infinitely more expensive to construct and it only takes one delay/accident and all subsequent trains after cause a log jam…vs a bus which can route around it.
A better solution uses corridors dedicated to buses that are electric powered.
Something like this was done in Colombia with these routes being connected by ground hubs, similar to subway stations.
That’s like saying a ship is more expensive than a car. It depends.
A tram is not „infinitely“ (what absurd statement is that anyway) more expensive than a bus.
Construction cost is not everything, and they’re not even that much higher, you also need to consider service life (much longer with trains), energy cost per passenger mile (much lower with trains thanks to the lower resistance), etc.
What is best is always depending on the specific circumstances.
The biggest limitation of buses is capacity, and a highly used tram is cheaper per passenger mile than a bus. Try replacing the S-Bahn in Berlin with BRT, see how far that gets you. You’d probably need to bulldoze a new highway… speaking of which:
Germany is actually hellbent on building a highway right through its capital Berlin, which currently clocks in at 700 milion € for 3.2 km. I expect the whole thing to end at ~2 bn € for ~7 km.
So I think the costs of public transport are really not the issue people should be focusing on.
You wouldn’t even have to go for the “replacing the S-Bahn” to show how ludicrous a BRT is as a suggestion, unless you’re not paying the constructors and drivers a living wage, which is why it makes sense in say Colombia and not in Germany…just think about replacing the M-lines of Berlin tramways with a BRT. It would have to be couple meters wider, would be terribly unreliable and inefficient, not to speak of noisy and bumpy. Now who would want to have that? Not to mention how much the upkeep of two lanes of dedicated BRT costs vs. maintenance of steel on steel rails and catenary. (Most of the time you’d find the latter to be cheaper.) In Helsinki, Finland we are currently waiting for a new tram/light rail option to replace a bus service that should have been a modern tram/light rail line in the first place: https://raidejokeri.info/en/ In the neighbour municipality Vantaa some parties were trying to push for a BRT option but the independent research suggested light rail/tram option to be the best and this is what was chosen: https://www.vantaa.fi/en/housing-and-environment/traffic-and-transport/vantaa-light-rail (they call it light rail but in some ways it’s also reasonable to call it a tram)
Electric busses are actually a lot more complex logistically than electric trains. With a train, you just need a bunch of big-ass transformers and overhead wires. Expensive to install, but very reliable and relatively low maintenance over many years.
Batteries on the other hand are heavy, relatively fragile, degrade quickly, and very expensive. With a 100KWh EV, about 1/3 of the total cost is the battery, so it would likewise increase the cost of a bus.
Charging is another problem, instead of the whole system using energy real-time, you now need a distribution system that can take hundreds of busses at night and charge them all back up, requiring a massive amount of power in a somewhat short time. While it’s nice that energy is generally cheaper at night, you still need the infrastructure that can take that load.
So, it’s not to say that there’s no place for them, just that our main focus needs to be on rail in most places. There are lots of low-density places with cheap power and temperate weather that absolutely need BEV busses, but a lot more with challenging weather, older grids, and medium density that are a better fit for rail.
IMO electric busses needs to have a trolley bus infrastructure on some route so the bus is recharged during the day. Won’t cover 100% of the energy needs, but will spread out the charging time.
I feel like I remember reading about tests on a roadway that could charge your car as you drive on it, like a qi charger. If that gets hammered out, dedicated bus lanes with the charging tech would limit the cost to implement to one lane while busses still have the freedom to reroute if needed.
Trolley buses do exist…
https://en.m.wikipedia.org/wiki/Trolley_buses_in_Vancouver
You can charge electric buses at termini though. Albeit this doesn’t change the challenges much. The electric buses are best suited for lines where the higher capacity isn’t needed and where the line is not likely to be longer than a little over 15 km.
Here in NYC, we switched to hybrid electric buses many years ago and are currently transitioning to all electric buses. I’m not sure about other cities. 
Yes, we certainly can route around it, but having lived in London for most of my life, I can tell you that we seldom route around it. However given the capacity that light railway how. If we keep the vehicles moving on the main arteries, we can move more people alleviating the frustration.
This is a common misbelief. Trams and light rail usually have points where the units can go around if one unit has derailed, unless the unit has tipped over, which in itself is very very rare. Good planning is crucial. “A better solution uses corridors dedicated to buses that are electric powered.” Nope, nope, nope. You have to present arguments to this claim, maybe then I can be bothered to counterargument such nonsense.
You have loops on the network for unidirectional or switches on strategic places to reverse in case of engineering works or incident.
Ah yes, and we can put those corridors underground in a big circle.
Like some kind of hyper-loop!