I never understood OpenTTD. Passengers just board your vehicles and go wherever you take them? That makes no sense to me. How is that supposed to work?
I've played a bit of Simutrans, where each prospective passenger has an origin and a destination, and if you can take them there, they use your services, otherwise they don't.
I think the logic is that they only show up at the station if there is a train that goes where they want. Much like in real life how the trains go on a schedule and you get on if it is going where you want.
Now I'm sure the simulation isn't perfect but it seems to make enough sense for game logic.
You can enable a feature called cargodist. This adds the functionality, where passengers have a destination in mind.
I think Railroad tycoon 3 had a good system. Cargo flowed towards a destination, even if there weren't methods to transport goods. Cargo would prefer to take the easiest path though, so if you built a rail line between a source and destination, the cargo would prefer the line.
It depends on a lot of factors, like the size of the town etc. traffic will increase if you make stations, promoting travel between cities. money can also be made by connecting factories with farms etc, fairly simple.
you can go way complex with orders, like only depart when 50% full or 100% full, to optimize your lines.
Passengers in OpenTTD are just a type of cargo like any other resource in the game. They're different from industry cargo in that the building that "consumes" them is the same as the one that "produces" them (residential areas), but there isn't any more to it than that.
Why does it need to make any more sense than that to be enjoyable?
I've played a bit of Simutrans, where each prospective passenger has an origin and a destination, and if you can take them there, they use your services, otherwise they don't.