Think miles per person per day. More dense means everything is closer.
Transport infrastructure (roads, buses, railroads, trams), housing, everyday service infrastructure (supermarkets, medical services, restaurants, haircutters) and employment infrastructure needs to be planned holistically or you're just shifting between problems - in the case of only going for denser housing, you'll lower homelessness a bit but get traffic issues in return.
And on top of that, city planning needs to take entrenched interests into account. Often enough NIMBYist complaints are founded in real fears of exploding traffic or a loss in property value - but these can be counteracted and compensated, if one is willing to.
Dense industrial areas are hard
I'd love that too, but it's not happening. FAANG isn't building their new HQ campus into the first floor of a new apartment complex. It'll be where it'll be and we'll have to fight through ever increasing traffic to get there.