People go homeless for many different reasons. Some times its just eviction. Eviction is when you get kicked out of your apartment. If your rent raises and you can't afford it and not pay for a month or two your landlord will kick you out.
The next reason is health and mental health. The medication might cost too much and then you can't pay rent so you get an eviction. So after you get sick and the hospital bills come in you have to pay them and not have as much money that you need for bills or for rent.
Another reason is addiction. When people get hooked on drugs or alcohol they can't get as much as they want. They spend all their money including savings getting as much as they can. When they go homeless they might spend the money they get from the street on drugs or alcohol.
The last reason is when they rent raises. They can't get a raise from their work and they rent raised. They are forced to get another job or go homeless.