How could they? What could possibly motivate them to act like that? Happens to everyone.
Being asked to take on a new role at work? What’s motivating them to ask for the switch?
Being treated poorly at the airport? What’s motivating them to do this to me?
Being offered free services that normally aren’t free? What’s their motivation?
Well, who cares about their motivation? It shouldn’t motivate your decision, reaction, or appreciation. Right?
[UPDATE] Who’s is embarrassingly spelled wrong. It should be whose. Thanks, @ERGreenberg. Sorry, Ms Ocar and Mrs Peterson. I’m leaving it.