My August earnings are less than half of what I earned in August last year, mainly due to a loss of half my Google traffic.
But EPC and CTR have also fallen considerably making it a double whammy.
My earnings peaked around 2010 after rising gradually since 2003, but are now a bit less than 2003.
I don't see IBAs as much of a factor on ECPM - they were only 5% of my contextual impressions last year (but 10% this year - mainly due to falling EPC I imagine).
CPM and third-party ads are less than 2% of contextual impressions so that would probably mean that re-marketing ads are not an influence on EPC in my case.
I would agree that factors affecting EPC/ECPM in the past few years could be, as others have mentioned:
1) more publishers competing,
2) advertisers bidding smarter or dropping out because of economic reasons,
3) ad blindness (including ad blocking, to a small extent).