It's MUCH cheaper than TV, radio or print, for precisely those reasons. But Corporate America wouldn't be moving in that direction if the advertising was all being blocked or wasn't generating business. And because the demographics of social media are a lot younger than TV, radio or print, that's all the greater incentive to stop casting the line into an ocean dominated by greybeards.
Oh, and if you make your ad "cool" enough, the younger demos will swallow the bait. It's the same old gullible/stupid customer that advertisers have always coveted, just using new media.