Just think of it like a really slow but never ending rebate. And if enough people do it, we'll even have a chance of lowering the overall profitability.
The 1060 6GB won't be worth $500 forever - in about a year, I'm guessing Nvidia and AMD will have stepped up their production and the price will have halved or less.
You'd probably make closer to £70 with your CPU thrown in, but it's all a gamble.
https://en.wikipedia.org/wiki/Tragedy_of_the_commons
For your argument to make sense, a single farmer's decision would need to have the ability to change the outcome, and it doesn't.
Otherwise not doing this makes about as much sense as cleaning a cup of coffee to save and orphan from a shark.
Further scale provides efficiency. If only 1/10 as many people use gas powered cars then gas stations become harder to find pushing more people to electric cars. Similarly as more people go off grid staying on grid becomes more expensive pushing ever more solar adoption.