Sorry, it was mostly for comedic purpose. A less jerk answer

• In a sane world blood shouldn't be a commodity.

• Even if it isn't a commodity but you still use money to incentivize donation, you run into the problem of "the law is equal for everyone, neither billionaires nor homeless can sleep under a bridge" wink wink.

Of course, blood save lives, and perhaps there are shortages of blood in countries where they don't incentivize donation with money, but I don't know if that's true.