Trams beat buses in almost every way.

Passenger UX: - railed vehicles only move and accelerate longitudinally (with a little centripetal force at the very predictable corners). Consequences: people will often choose to stand even while there are free seats. Trams are so smooth that standing feels comfortable. (If you preference is to sit, you benefit too.)

- modern trams have lower floors than any road vehicle can realistically achieve (especially if built for use on random roads). They're near flush with the curb at tram stops, which is nice for accessibility (prams, wheelchairs, people with granny-trolleys for shopping).

Pedestrian UX: - trams follow tram paths, predictably. Once you're used to them (which doesn't take long), you'll stand just centimeters from a passing tram and feel completely comfortable about it. As a pedestrian, no transit line is as easy to cross as a tram line. (Certainly not a bus lane!)

Land use: - since trams follow rails without any lateral deviation or wiggle (and bonus: they're rather narrow), dedicated tram lines require about 40% less land than bus lanes. Especially on streets where there might not be much free lane width to spare, that counts!

Tiny operating costs, negligible marginal costs: - there's a far higher ratio of passengers to driver in a tram - electricity over wire makes the marginal cost of energy to operate negligible. Once the infrastructure is there, and once the tram is running, the frequency of service can be increased and the operating cost can get arbitrarily cheap.

Transit capacity: - road intersections are the capacity bottleneck in any road grid. Behind them, queues form and grow (congestion) until a point where the expected time (much of it queuing in traffic) presents too high a cost for the marginal journey to happen. - trams can pass at same gauge while scaling up intersection capacity by about two orders of magnitude, allowing much more rapid movement of people with much less urban land and less infrastructure

(buses with dedicated lanes could hypothetically deliver this, if buses were as popular as trams and operated like trams in dedicated lanes)

Air pollution: - the primary source of most urban air pollution is road vehicle abrasion (tyres on roads, brake dust) and road vehicle combustion engines. Getting rid of combustion engines solves less than half that problem. To stop primary emission of particulates, you need to solve tyres and car brakes. Railed vehicles do that: clean air. - a large part of air pollution is secondary: particulates settle on the large road surfaces comprising much of our cities. Then road vehicles with large tyre surface area (and varying lateral positions) run over the surface, re-ejecting that dust up into the air.

That air pollution is killing people (estimates vary: somewhere from 'many months' to 'a few years' of life expectancy are lost to urban air pollution). Trams get rid of it completely.

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The biggest problem with trams is that they require competent civic administration, with a steady pace of long term infrastructure investment (boom & bust would destroys the capacity to produce & maintain trams & infrastructure economically), financed at competitive rates. They also benefit from very high urban walkability in the vicinity of potential tram stops, and high density of development (including housing). Not many cities have that.

Some cities do, and their trams are a dream: https://www.youtube.com/watch?v=t4Ph-L4Mbt4