Trams have a much higher capacity then buses: https://bathtrams.uk/relative-carrying-capacity-cars-buses-trams/
Utrecht has the busiest bus network in the Netherlands, impacting the air quality in the city. Studies have shown that the bus network has reached a saturation point and is no more a viable solution for the growing passenger traffic in the region. As a result, a tram network was seen as a more practical alternative public transport system as it can carry up to five times more passengers than a bus. Furthermore the triple bendy bus, below, simply did not have the capacity to take people to the University Science Park.
Utrecht triple bendy bus
Trams have much higher capacity than a bus: