Local city traffic means a lot. It’s income, you can get some decently profitable lines in city if done well, and they feed city to city traffic and deliver it as well. With the 20 minute rule you don’t only need to get the person on the train, but they need to get to their destination. Good local traffic means more change for them to hit their destination and take the route again, which means greater city to city traffic.
It does indeed… its not just about getting a civ to the centre of another city, they have to make it to their destination too.
If there is a long walk to each station from home > station & station > work, then they will drive.
If they drive and get stuck in heavy traffic, that civ will not decide to use your lines again until they make it back.. hence why it can take years before you see the effect of a more optimised route. You have to give them chance to get where they are going first before they re-evaluate how they intend on travelling the next leg of their journey.