irl when you make an apartment building the ground floor is used for commercial purposes (you can have banks, restaurants, clothes stores, butchers, surpermarkets, whatever...) as you can see in the photos I linked.
Even more, you can buy (or rent) an appartment and make it an office for your business, so, appart from industrial zones, everything is mixed irl
The developer is European idk why the game focuses only in american style city planning that are highly inefficient and car-centric. You barelly need a car when you have access to all kind of services at 10 or 15 minutes walking
The ingame "High density residential zones" should include some type of commercial activity in the city to be more realistic