If a trait is not well adapted to current local conditions, what might be the reasons why it is not, and how might one check to see which of those reason (s) is correct?

Non-availability of a proper niche to inhabit an environment can be a reason of non-adapting of local conditions in a trait. This may also be due to the filtering out of the trait by the environment. Further, other traits which are supporting the growth of the organism in this particular environment may be acting as crucial and significant to the survival, as compared to this trait