Actually I think he is saying that they need their advertising revenues to grow in order to maintain perceived momentum in advertisers' minds, in order to have

Actually I think he is saying that they need their advertising revenues to grow in order to maintain perceived momentum in advertisers' minds, in order to have revenue at all. So it's more drastic than what you describe, assuming of course that the OP is right and that retention of FB advertisers is null (which I'd love to see data about).