The numbers they need to look at are the decrease in number of farmers since 1920. Back then a family could survive on 80 acres but as time moved on the 80s were bought up and became 160 then 240 and now a single farm can be 1000's of acres. Often a farmer might not own 1000's of acres but will cash rent or crop share other's land. Just looking at the decrease of black farmers without equating that number to the decrease of farmers in general is meaningless.
The cost to get into farming today beyond the actual land is astronomical. We're talking millions of dollars for equipment to do row crop farming. Listen to some of the numbers on Cole the Cornstar vlog. To successfully farm you need knowledge of government rules of which there are many, bookkeeping, financial planning, farm taxes, how to operate all the equipment, mechanical to do repairs, special training to be able to apply chemicals, ability to cope with crop failures, marketing and a zillion other details, Raising livestock or specialty niche farming each needs it own special knowledge and hand-on experience. This year Iowa farmers were treated to drought and a derecho really fun times and the taxes, operating and equipment loans, fuel, seed, chemicals, etc. all still need to be paid.