Your city actually does have maximum/high-density buildings hence the darker blues found in the image where you show your density. As you probably already know, your city is mostly poor that's why the population is so high. I actually want more poor residents in some of my cities, but to the extent that you have yours.
Are you expecting taller, more modern looking buildings? Those only appear as your city's wealth increases, therefore you need more parks but expect a major population decrease as the wealth of your city increases.
Good luck friend.
Thanks for the reply. Yeah, the city is almost completely low wealth. I've been experimenting with that the last couple days. Not sure if there are benefits to having higher wealth citizens I don't know about.
As for the density, every building I click on is listed as medium density. I can't find any high density buildings in my whole city. I tried dezoning some areas to create more room, in case there was a space problem, but it didn't change anything.