I believe that all 50 states require real property transfers to be recorded. Chief reasons nowadays would be taxes and liability. The tax bill is the responsibility of the last owner of record, as the county can’t mail it to someone they don’t know about or put a lien on a property if they don’t know whose it is. If somebody gets injured on a property, or there’s a toxic waste spill, the last recorded owner of the property is the owner — neither an individual or government agency can bring suit against someone they can’t identify. If people were allowed to have private written instruments serve as valid land transfers, loss of a piece of paper (say in a house fire or tornado) could eliminate the only proof of the transfer, and all hell would break loose in cases of ownership disputes. And just imagine the chaos back in the days when the federal government was giving away land under homesteading laws, and many farmers were illiterate (and look how the Indians made out, with their lack of recorded land titles).
People can do an unrecorded land contract and own the land. As long as the contract is notarized, it is legal and binding. That is why there is title insurance, to protect against prior claims to land. I have done mortgages in KY and TN, and I have seen land contracts not recorded for a decade. It is perfectly legal.