how do you explain 50-75% drop in CPC compared to 10-12 years ago?
Pretty simple. Ads 10-12 years ago where higher quality. Folks had more disposable income. G had not yet changed the game, learning over time where they could cut yours and make theirs...
Today, even stupid users won't click ads since they don't have any money to dispose of (too busy getting heat, fuel for cars, or simply buying food at the local market).
Things will get thin as advertisers are withdrawing their budgets, scaling back, and probably laying off workers as well.
Believe me, I would love to be proved wrong, but past experience has shown all too well that when money is tight ALL OVER FOR EVERYONE INCLUDING GOVERNMENTS it will trickle down to the lowest levels of income potentials.
ONE WAY to get through something like this is to grab bootstraps, cold-call, find, or court and corral local or regional businesses to buy ad space on your HIGHLY VALUED AND POPULAR website---an advertising pitch that could benefit from an exposure on your world wide internet property. In fact, that's where I made most of my money, back in the day, with adsense only a minor thought, at best.
YMMV