I literally raise money and build homes for the homeless, so hopefully I can add some insight (and I am not really from the sector - so I had to learn all these concepts too).

Essentially people who are chronically homeless have a range of issues that are keeping them from being stable enough in their lives to manage a property on their own. This can be due to chronic poverty - never learnt to read and write - neither did their parents etc, therefore no stable income, no stable structures when growing up, and so the cycle obviously continues. When you are in this position its also then more likely that when things go bad you end up homeless, and then with no skills or necessary experience to change your own circumstances, you just cycle further and further out of the traditional support systems. Hence "chronic".

E.g. How do you earn money when you don't own a phone, have a stable place to live and can't even really read or write - (or not very well), so this cycle just continues. Other times it is drugs, alcohol or mental health issues but it can also be from things like those fleeing family violence, those with disabilities.

I live in Melbourne, Australia, our current rental vacancies (city of over 5 Million people) is less than 1% and of all the properties available, at any one time, only 1 or 2 of those are actually classified as affordable (not costing more than 30% of your income). Our avg. House Price is over $1M and our Social Security is around $250 per week if you are on benefits. There are 2 places for rent in all of Melbourne for under $250 per week and both of those are student accommodation (essentially a single dorm room).

All of these factors impact their ability to remain stable (in the context of self management) so typically what happens is they just default back into homelessness as they have gotten to the point they know no other life and then don't know how to not be homeless. Sometimes even a roof over heads doesn't help unless service organisations are there to help.

Edit - grammar