You could be correct that only legit users clicked the FB ads and upon review of my site they had no interest in using my service or my pricing scared them away (or any other legit number of reasons).
However, it would be willful blindness to ignore what I can verify vis-a-vis the FB paid promotion. Moreover, when I can verify the majority of likes are from illegitimate users/profiles, based on not having any posts and otherwise being inactive, then I have no expectation the users clicking the ads are any more legit than users clicking the promotion. If FB had faith this was not the case I see no reason they would not disclose the users who clicked the ads so advertisers could confirm their legitimacy.
There was a video released recently talking about fake accounts and clicking on paid like ads. It explained pretty well why they do it. That doesn't really carry over to other paid ads though.
As for the second part probably because it's a huge privacy violation.
However, it would be willful blindness to ignore what I can verify vis-a-vis the FB paid promotion. Moreover, when I can verify the majority of likes are from illegitimate users/profiles, based on not having any posts and otherwise being inactive, then I have no expectation the users clicking the ads are any more legit than users clicking the promotion. If FB had faith this was not the case I see no reason they would not disclose the users who clicked the ads so advertisers could confirm their legitimacy.