None of your senses detect *things*. Instead, they all detect *changes* in things. That’s why a pool feels cold when you get in (because that’s a change), but then it doesn’t feel cold anymore after a while (because nothing has changed).
Scents come from molecules in the air hitting your nose. If the same molecules keep hitting your nose for a long stretch of time then you stop smelling them. This is why you don’t smell what your own house smells like.
It’s also possible that the source of the volatile molecules has simply stopped producing them.