Most sites that do retargeting do it based on number and stats. They know that if a rando that visits their site (but doesn't buy anything, doesn't sign up for a new letter, doesn't click on contact me) will convert at X percentage if they show him an ad.
So they do the math to figure out what that looks like after impression 2, 3, 4, 5, etc... somewhere there's a point at which the cumulative conversion percentage doesn't go up or goes up so slowly to not justify the cost and they stop.
So what seams like a big waste of money to you, seams like a profitable business decision based in fact to them.
Certainly this seems like the way it should work. In order for it to actually work like this it would require the marketers to actually understand retargeting rather than believing the hype spread by ad networks, and it would require the inventory to be delivered through systems which could provide adequate tracking.
Click-though is often not the expected success criteria for these ads though, instead they depend on overwhelming you with reminders until you crack. This has two consequences, the first is that successful campaigns are absolutely designed to annoy you and not give up at a point which is decent, and secondly the tracking becomes extremely weak, with high rates of inferred success where the retargeting ads may not have had a positive influence at all.
Most sites that do retargeting do it based on number and stats. They know that if a rando that visits their site (but doesn't buy anything, doesn't sign up for a new letter, doesn't click on contact me) will convert at X percentage if they show him an ad.
So they do the math to figure out what that looks like after impression 2, 3, 4, 5, etc... somewhere there's a point at which the cumulative conversion percentage doesn't go up or goes up so slowly to not justify the cost and they stop.
So what seams like a big waste of money to you, seams like a profitable business decision based in fact to them.