The issue is simple, the network cannot handle the numbers of passengers at certain places and times now (let alone after any developments like the NS that will increase ridership) because of the way the network was designed and extended. They can’t really do anything so can’t say anything. When you’re at a station waiting because your tram hasn’t turned up, it’s because it got stuck in an issue somewhere else on the network, sometimes right across town. Adding extra trams might mean you get a tram turning up sooner OR it means those trams cause the system to snarl up even worse meaning no benefit or worse service. It’s like an electrical circuit, you can only put so much through it before it blows and it then needs fixing.
This is why they are talking about three underground tunnels across the city to handle trams and trains. Manchester has exploded in sizr and is continuing to do so. You can see a video here which explains some of it
https://www.skyscrapercity.com/posts/195371973/.
Sadly most of us won’t see this happen even if something like this goes ahead, and that’s going to be hard to convince the government to release money.
In the meantime, it’s buses that will take the strain.