Most people don't want to travel long distances in a slow bus that stops every few hundred metres. So to get decent numbers of people onto public transport, including those who have a car available, something fast and reasonably convenient is needed. This does also mean that people will use what they see as a better alternative and transfer from bus to tram. If they didn't then there would be more and more cars, the buses would get stuck in traffic, become even slower, lose passengers, get less frequent, lose more passengers, put more cars on the road and so on. This isn't good for those who are unable to drive and reliant on the bus.
The ideal is to have a fast and frequent backbone to the transport network, which in most places is rail-based although bus rapid transit (with infrequent stops) does the job in a few. The buses would then provide the local links, feeding into this network at convenient interchanges but ensuring as far as possible that everyone is within a few hundred metres of a convenient stop. Most people travelling longer distances would get a faster journey with no cost penalty thanks to integrated ticketing. Any change is going to disadvantage some people, and someone who makes very long journeys on a bus, is happy with the amount of time this takes, and seems to have an aversion in principle to trams may turn out to be one of them.