This would have nothing to do with the effect shown. Paid clicks (i.e. the number of actual clicks on ads) have been growing rapidly over the same time period. Dropping CPCs are pretty obviously a result of the mix shifting to mobile (particularly since both mobile and desktop CPCs are rising).

> ad blindness

This is so true. I went to advertise on reddit the other day and was surprised when I realized that the ads I was buying were for the "Sponsored Links" at the TOP OF EVERY PAGE, but I trained myself to not see them 5-6 years ago and hadn't really seen them since. /scratches head.

That would be reflected in CTR rather than CPC.