Passengers will still take the quickest route to their destination. Which later in game, is via car, because cars are quicker overall. No walking to a bus stop, to go to the station, to then wait for a train, then ride it, to then catch a bus to their destination.
One exploit, I shall call it, is to make roads you’re not using for busses or trucks, extremely windy and long, and use the slowest road available. So it’s no longer quicker for car travel.
Or use the no main connection mod, and remove them entirely. Lol
Otherwise,you need to use small low capacity, but fast cheap trains so there’s no waiting at your stations.
But then the running costs will get you eventually.
Basically, how the game is, its so far for me been impossible to fill a 200 capacity modern train, without exploits or mods. Lol