You are not entitled to know anyone's reason for selling. However, everyone knows the buyer will find ways to ask this question to assess the motivation of the seller. This is attempt by the buyer to gain some advantage over the seller. It is always a good idea for the seller to not be present when a potential buyer is present.
A professional can look you straight in the eye and without blinking respond, "The seller has "experienced a life change/Starting a new chapter/is moving to a new location" that requires the sale of this home." That of course is not an answer, but the message should be loud and clear.
"Are you here to buy a house?"
Best of success to you.