It's probably because the game world is pathetically tiny (compared to real world), but the developers still want players to feel like it's full scale.
It's not really an issue of how big think we much as it's a limitation of hardware, software, and time/money. The world can only be so big before computers melt or the game crashes trying to load everything. And game developers only have so much time to fill the world and optimize the game.
The map size doesn't need to be bigger. It's already pretty large, especially when you consider the verticality and amount of detail and interiors the game has. Sure, games like Elden Ring dwarf it, but ER also has tons of empty natural landscape, so it's not nearly as taxing on HW or development time to create.
I hate the speeds on cars and bikes too. Whoever decided to say cars and bikes are going well over 100mph has clearly never been in a car going over 100 or seen videos of cars driving on roads going over 100.
There's nothing to investigate about it, polygon. They made it very clear that you are meant to enjoy the sights on a relaxing metro. We call it "immersion".