There are at least 8 active homeless shelters in the city - how are people still sleeping on the streets?

Genuine question. Most of them have A LOT of beds available. So, what is keeping people from finding shelter?

Edit: From the comments, it seems that the consensus is that the people wanting shelter can find it but many people choose not to. I suppose that leave the question of how much society should feel obligated to offer help to those who reject it?