What’s the point of the game then?
I mean, it’s about trying to make your lines as efficient as possible. What fun would it be if agents would wait for hours (real time) to get from point A to B?
It’s not like it is impossible to let a line have only 20 minutes of waiting time, in fact, it’s really easy. Most of the time 1 vehicle is already faster than 20 minutes and just adding another vehicle could do the trick.
You wouldn’t wait 4 hours to get to another city by train either, would you? And 4 hours would probably be a couple of years in-game time…