Seems to me like the reason for this is that most indoor rooms are expected to be scentless in the first place. People might also look at you funny for stating out of the blue that a room is well lit. On the other hand if I enter a barn and there is no scent at all, saying it would not be that weird.

There’s a scene in Brooklyn 99, or one of the characters sniffs and says, “what’s that smell?”

“That’s the absence of urine,” is the reply.

“Ah, finally some fresh air”

Phew, I’m glad that bad smell is gone.

One of the best lines in Ghostbusters:

Listen! Do you smell something ?

“What an odorless room!”