Consider the plight of a policy-maker who changes their stance on some issue. They may have changed their mind in light of new information, or evolved their position as a result of deeper reflection, personal experience, or maturation. Opponents will accuse them of "waffling" or "flip-flopping", indicating a lack of reliability or principles (if not straight-up bribery). Elected officials are responsible for expressing the will of the people they represent, so if they're elected largely by proponents of issue X, it is arguably a betrayal of sorts for them to be as dynamic as private citizens.

This is tangential to the original topic of insider trading, where the corruption is structural / systemic -- akin to how "conflict of interest" objectively describes a scenario, not an individual's behavior.