To be clear, all moments of avoidance are not necessarily bad or inappropriate. No one has an obligation to share or discuss something that isn't any of the business of the person inquiring about it. There are, however, moments of topical avoidance (shunning) that are illegitimate.
When a party to a relationship has a legitimate interest in a particular topic and asks about it, a responsive answer is due, as a matter of courtesy and respect. Sometimes a discussion is due. This establishes and maintains a level of trust between the parties.
When moments of appropriate and legitimate inquiry arise, they fall under the auspices of a type of social contract shared between the parties.
Relationships involve expectations. Successful relationships involve reasonable expectations that are mutually understood, shared, and consistently followed. The right of fair and legitimate inquiry and responsive discussion is among the reasonable expectations that are shared and consistently followed in successful relationships. Avoidance of fair and legitimate inquiry and responsive discussion is a clear sign of a relationship that is poisoned with manipulation and hidden agendas.
Almost invariably, the game of illegitimate avoidance (topical shunning) will also, necessarily involve the corollary game of gas lighting. No one who uses the device of topical shunning is going to own up to the fact that they are using it. That is one of the topics that must be shunned. Accordingly, a cover story or excuse for the fact that topical shunning is going on must be contrived at the expense of the victim.