The OEM does not do the financing. They 'might' have a company named 'Kubota Finance' that is really owned by "Household Finance' or 'GE Financial'. Cars are the same. The loan is not 'Made in Japan';.
When a vehicle contract is sold to the financing arm and is a zero rate loan, the OEM provides a holdback, a monthly payment to the financing company to make up for interest not earned. This is why you can buy at zero percent OR get a rebate.
For informational purposes, you can... do a sim0ple interest loan calculation, see how much in interest at a low rate (4%) you'd pay over say, five years. Compare that to the rebate. In Kubota world, you have to also factor in the value of KTAC too.
For some, knowing you own it from day one, not having to make that monthly payment (or debit) has value as well. Peace of mind.
Ass, grass or cash, no one tractors for free.