Although sometimes a move is necessary solely for career advancement, it is more common for people to consider new employment due to some negative experience with their current employer. However, it is never a good idea to dwell on this too much in an interview.
No one should tolerate an environment that is undesirable; and looking for another job is one course of action that can remedy the situation. Just keep in mind that sharing too much in an interview actually hurt you because you can come across as a complainer or generally create an aura of negativity.
When asked why you are considering a move in an interview, it is easy to fall into the trap of unloading all the trash about your current employer but this could be a costly mistake. When faced with such a question, you should share as much as necessary to articulate a legitimate reason for considering a move but don’t go into more detail than necessary. Yes, the interviewer might be intrigued by the gossip but in the end it comes across unprofessional, negative and could cost you the job.