Liverpool

Trams can generally hold more passengers per vehicle, and are more energy efficient (because steel rails are much lower resistance than rubber tyres on asphalt). They're also much easier to electrify (battery buses having lots of drawbacks, and overhead line driven trolleybuses being a complex and niche technology which nobody wants to deal with).

Not an inherent advantage, but the nature of them means that they often have much larger segments of exclusive right of way (i.e. tracks which aren't shared with road). Whilst there's nothing stopping you building loads of grade separated bus lanes, politically and practically it's much harder to do.

There's also an argument that people are more likely to use a tram than a bus just because they like them better, and that the presence of the tracks makes it easier for people to visualise the routes making the journeys easier to navigate.

The downsides are that you have to build a load of expensive infrastructure up front, and that they're more vulnerable to disruption such as obstructions on the track or road/line closures which they can't route around.

trams require physical infrastructure above and beyond the bus.. its seems like hes got an ulterior motive that depends on that infrastructure.