Aside from what anothersimulacrum and I have written a few posts back, there’s also a file size problem.
For example: Let’s say, we make cities the distance of Wentworth to Warren (two cities that are pretty close to each other; 7 km or 4.4 miles). Based on the lowest possible driving speed of 6 km/h, (which usually covers one tile, we can be generous again and say it covers two tiles), that would span 3500 tiles.
Since every overmap tile is 24 tiles and every overmap is 180 overmap tiles, you’d need to move almost a full overmap to reach an other city (146 overmap tiles).
If you’re lucky and can move in a straight line, that would generate and save 6 (reality bubble) times 146 overmap tiles to your computer, only to move from one (close) city to another.
Although people usually have hard drives with TB of storage capacity, I’m not sure everyone would like it if they get filled with files of “empty” space.
And that was an example of two cities that are close. Imagine driving from Manchester to Portland (~ 150 km / 100 miles)!
Now, while that would make some visible impact on your electric car, it also will drown your harddrive in “useless” files…