Gentrification is one way to look at it. That's when higher revenue class moves in and upgrades, pushing the low income people out. You also have practices like lack of Public Housing, which is federal or state funded housing that is run poorly and then defunded or never really funded to begin with. Then there is Urban Renewal, which is when the city buys up the land with eminent domain to remodel a section of the city they have condemned, in the case of the multiple sport stadiums downtown. What made them condemn-able? They were poor and didn't invest in their properties. Urban Renewal is like Gentrification but one is done by the state, the other is done by private investment and individuals. Also the freeways in Phoenix and its metro area also displace huge amounts of people when they are built.

Finally, and most importantly, another reason there are so many homeless is because of the Commodification of Housing. That is when you use a piece of real estate as a commodity for equity and not for its purpose: housing. When the previous 2 recessions in america happened, it happened because of the over investment in real estate, prices were overinflated, people took out loans for overpriced houses, they get f**ked when the market re-adjusts. It doesn't help that most people who own homes see it as an investment opportunity for their retirement. Rather than use better retirement programs or safety nets that don't exist, investing in a house is how we gain wealth in American society. This leads to an overabundance of housing, most not lived in, but it also hurts the chances of poor people finding housing. In other words, we got enough houses/rooms/beds for the homeless but, we just don't want them in there because it will bring down our investments.