Demand for zoning means many things in Skylines 2. If someone builds a house in your city, someone needs to occupy that house. If nobody lives there after a certain amount of time, the house will be marked as Abandoned and it will eventually collapse, and it will need to be demolished. Demand is driven by how many people live in your city, how many jobs there are, how many workers there are, what their education level is, how many amenities there are, etc. These factors are presented to you in the zoning view. It isn’t a calculation you can shortcut: if you force demand to the maximum values, houses will be built and there won’t even be enough citizens to occupy them. You need to fill out your city with other zoning types, service buildings, transportation options, and so on.

Infinite Demand for zoning isn’t a bug fix, it’s a cheat code. The problem may be that how demand is calculated in the game needs adjustment, but maxing out that calculation at all times is not a long-term solution.