Fabric softener is a product that is added to laundry water to reduce static cling, improve softness and reduce wrinkles in fabrics. It contains conditioners that help to coat and smoothen out fibers, making them more comfortable against the skin.
This is the same reason why you shouldn't use fabric softeners with CD - s. (backtocalley.com)
Occasionally you will find that too much detergent or the accidental use of fabric softener sheets can cause excessive odor or repelling. (the-cloth-diaper-connection.com)
The sickly sweet floral scent of fabric softener used by the previous owners was so strong that I had to rewash the clothing multiple times before I felt safe using it to dress my son! (thehealthyhomeeconomist.com)