The biggest difference between blood and organs is scale. Organs are sold for largest sums of money which means that there is much more money and time available to do full medical work ups and tests to verify the quality of the organs.
As well as a significantly stronger motivation to deceive in order to secure the payout. Assuming that verification procedures against a hostile donor can maintain quality vastly overestimates the tests.
The deception is made more difficult via the significant match screening required. When I donate blood, they ask me a series of questions. I can answer as truthfully as I like. How much testing they do to the whole or processed blood likely differs widely from facility to facility.
Before donating a kidney, I went through half a dozen invasive, detailed medical exams that didn't depend on my given answers at all.
