One thing to consider too is scheduled events. Imagine a couple towns get together and throw a fair along a route that connects them, and you get to see celebrations and games and vendors who might sell trinkets that are hard to track down otherwise. Perhaps the local monarch goes on a hunt with the massive party of servants and knights that might entail, with different practices for different cultures. A band of cultists clears an area for several days leading up to their yearly ritual. It’s migration season for a certain species of animal/monster. There are so many possibilities!
Even just vendors passing through can be made more interesting. Do they carry their wares via backpack or cart? Are they being attacked by bandits? Wild animals? Are they trying to smuggle goods or services somewhere?
It all has to be programmed of course, which is the main holdup on what makes it so hard to flesh out those parts of the world.
I do also see weight in the idea that, past a certain point, traveling is just boring, especially if the only thing of importance is the Main Story Quest. Travel is also often boring in real life too but we can tune it out, or find little ways to pass the time and entertain ourselves during the more mundane moments. We’re not frequently afforded that luxury in games. When you’re playing a game and dealing with the downtime going from point A to B, often there is literally nothing to do except hold down the movement keys and deal with the occasional path change/obstacle.
The point of games is to be engaging, and if there’s nothing to do while traveling but look at the scenery and surroundings it will eventually get boring. Even if the travel gets interrupted occasionally for an encounter, I think it’s arguable to say that the content is literally not travel anymore and in fact papering over a bad travel system (if the only thing interesting is the stuff you find that you have to stop and take care of). Adding more unique/transient stuff along routes is only half of the battle; work has to be put in to make traveling enjoyable in and of itself for players to want to do it instead of skip it.
But as always, the best solution to our problem is to simply add more trains.