Thank you for the opportunity to help you with your question!
It is because they are afraid that someone coming out of rehab may may fall again in the problem they are avoiding. In order to handle this situation, someone professional is needed to coordinate the resources essential for safety both for treated person as well we inhabitants of that house. If necessary, these resources can be provided at the rehab center to make patient at ease and comfort without risking it from hapenning again.
Please let me know if you need any clarification. I'm always happy to answer your questions.