I have noticed this with my cities. I just bought the game, so I'm certainty not an expert. However, I have built three cities and read am I could find online about the game.
That being said, I have found that the utilities could be too expensive, the other zones could be producing too expensive and those needed goods cannot be acquired, the type of zone isn't wanted (try a lower density office zone).
Lastly, it could be the quality of life which sounds probable since it appears to be a radius/area issue.