- You can invest around them. Because unlike a bus, a tram can't just be upped and moved somewhere else developers are able to build housing and services confident that there will be service.
- They are easier to segregate and run at speed so that you can run limited stop services that are credible. I suspect this is what you are getting at with airports, but I'm not sure why you think an airport is the only reasonable use for fast limited-stop operation
- They can carry more people easily. 2 or 3 car trams are the norm, and the smoother ride and increased safety means that it is much safer to carry lots of standing passengers
- People like them. You can actually get people out of cars onto a tram, where faced with a bus they will assume that it is going to be dirty and they will be robbed (however untrue that is)
That is not true in some places. MN built its light rail in such a way that interacts with normal traffic quite a lot (including killing people because of a really badly designed interaction on a former turn). I get the feeling someone in the planning office had taken no lessons from street cars.
The key reasons buses are better is that they can go where people need to go and are not locked in to where they are built out at.
The sad part is that in many parts of the world ridership doesn't increase much with the cost going down, even to free. hopefully autonomous fuel cell / battery cars and buses will make point to point more manageable and viable overall.