I agree with the OP. Why on earth would they go out of their way to SOLICIT people to move? That would really burn me if I were seated in an exit row, which presumably I booked in advance, and was presumably blocked until the seats were released to airport control.

I feel differently about a GA placing somebody there (either because the flight is full or because somebody asked). That's totally fine with me. Less fine are the "seat lice" who wander up as soon as the door is closed and decide that the seat next to me looks better than the one they had assigned. And worst of all would be this FA, in my book.