The counterfeits are being sent to shoppers who were specifically looking for genuine apple products (I agree I've heard bad things about Apple's strain relief) so presumably the quality isn't the problem for these buyers.
If people are walking by an apple store every day, but go bargain-hunting on the internet when they need an Apple product, then sure. Lower the price, get the customers away from Amazon, and you can make sure they get the genuine item.
But if customers are going to buy from Amazon anyway, it's impossible to drop the price far enough to make counterfeits unprofitable, because counterfeits can always be more profitable as they can target lower specs.
If a 2.5A fast charger costs $10 to make, and a shitty 500mA counterfeit costs $5 to make, the counterfeiter will make 100% profit even if the legitimate manufacturer sells at the cost of production.