The decline has also other reasons which is market penetration. But yes, the loss caused by bad tracking is huge.
The main reason is IMO the dodgy affiliate software that is not combined with the antics of the operators themselves. The oldschool systems like 5dimes still track well. The old proprietary simple tipico had perfect tracking; the Neterefer tipico is **** etc.
Most of people do not use the privacy centered browsers and even the amount of people using adblocks is not on the scale that explains the big drop.
The last nail to the coffin will be once Chrome will implement their own adblock, which is something they already started (they block ads or even wesbites they find "misleading") and something they will work on unless they are stopped (my friend, owner of ad agency, is suing Google atm). But affiliate industry might kill itself before Google does it. It is a thrilling race.
We are all bloodsucking ticks, hungry, devious
each one latched on to the ass of the previous
when the last and the first latch on it can be shown
ass-blood sucked by the first from the last is his own