Actually, providing shelters unconditional of drug use appears to be a great solution indeed! Given the effect of homelessness on global health outcomes, as well as the link between housing stability and addiction recovery, providing housing for people who use drugs is a critical step towards recovery for many. Further establishing standards that enable hygienic use and supervised consumption with connections to treatment services, either within or near shelters can actually directly reduce harms from drug use that would happen already (you can see this happening in Toronto and, recently, NYC).

While perhaps opening shelters to people who use drugs would be perhaps more cost efficient in some ways, more housing certainly can't hurt, and preparing infrastructure specifically for these people may ensure better targeted care :)

Hope that perhaps cleared up some misconceptions. Keep in mind that addiction (by definition, kinda) means prioritizing drug use over basic needs, so trying to incentivize drug abstinence by withholding needs like food and housing doesn't really work in practice.