Homelessness and Prostitution are strongly intertwined; it is a grim and ugly reality. Some of the factors contributing to it being a blind-spot is due to the fact that it does not fit our "expectations" of prostitution. The classic stereotype of "pimp and hooker" is just one of the many situations on the streets. Prostitution does not always involve an exchange of favors for currency.
"The most common is called ‘survival sex'. Typically, a person will offer a homeless youth a place to stay and expect sexual activity in return. Sometimes the teen is not aware of the arrangement until after they’ve stayed with a person for a few days or weeks". - Chris Mirabal (program manager of Looking Glass New Roads Youth Shelter)
This exploitative behavior is not limited to the female sex. Homeless males are also being pushed into these difficult situations as well: "They wanted to have, like me have sex with her, while I’m staying on their couch, as part of rent. I was like, I can’t do that. I’m sorry." - Brain ( 21 years old) He admits that his age and gender made it easier for him to say no and leave that situation.
Living in lack of resources can drive people to desperate measures. In addition the possibilities of mental health or substance abuse can make the situation worse. When you don’t know where your next meal is coming from/or if you'll get a next meal it becomes easier to rationalize things like this.