I feel like that might be because the routes only have about 5-7 days in them (depending on patreon or not). This is technically Walter's first time meeting all of them, where as most visual novels have their characters as already established friends, or just have a lot of time skipped (Adastra), so they have a lot more groundwork to do for themselves. The only one that isn't a complete stranger is Gil, who Walter had actively avoided for the most part in highschool anyways. What character developement there is are more like hints, not life changing revelations. It's waaay too soon for that anyways. Gotta get invested in the characters before they start talking about their childhood traumas.
I feel like it also might be dependant on just how into the story you can get. Which depends on personal opinion.
I'm curious as to whether or not you have a specific visual novel in mind when you talk about good dialogue. What would you say is a good example of a game who does dialogue well?