Why are somethings odorless?

Answer 1

Odor is a human sense (or an animal sense),

if you lack the organs for detecting it, then a substance is "odorless" ... to you.

Note that (for us mammals) a substance must be in vapor form to be detected,

thus solids lack odor in general, while heating intensifies odor.

Answer 2

Some substances are odorless because they lack molecules that can evaporate and stimulate our olfactory receptors in the nose. Odors are typically caused by volatile organic compounds that are released into the air and detected by our sense of smell. If a substance does not contain these volatile compounds, then it will not have a detectable odor.