Why does my foam blanket not smell clean after I wash it?

I have one of those foam blankets, the kind that resembles velour. I wash it in the washing machine with detergent, and put it in the dryer. It comes out of the dryer not smelling clean. Everything else that I dry in the dryer smells fine.

Why would a foam blanket not smell clean after being washed? It’s washed a lot, so it’s not like it’s extremely smelly when it goes into the machine.