Growing an organ means you need it to genetically match the person, have all the different tissues hooked up together correctly, and somehow grow it faster than

Growing an organ means you need it to genetically match the person, have all the different tissues hooked up together correctly, and somehow grow it faster than normally happens. And you need that fast growth to turn off before you put it in someone. Growing a vat of meat tissue just means you get a lot of cells to absorb nutrients and reproduce. It's likely multiple magnitudes easier.