Math is a thing. 0% is an advertising technique, but it is also a way for lenders to make more total dollars available to lend. (That part is a regulation thing)
You have to do the math on every deal. In some cases, the 0% is still a way better deal than the cash back. In some cases it is not. Most of the time you are better off taking the 0% and investing the cash. 36-84 months from now the recently dropped stocks will rebound. Over the last 50+ years the market has averaged over 10% ROI. If I buy a 100k tractor over 7 years, that would allow me to invest that money and make something in the neighborhood of 50k over those years...after losing some to inflation. Paying cash, even getting $10k cash back would still be a losing option financially.
All dealers do NOT pay the same wholesale. Most manufacturers offer their best dealers all sorts of incentives. Sometimes they also offer incentives to new dealers to help them get started moving product. On top of that, some dealers go for higher volumes with lower margins; others want higher margins and sell fewer units.
Dealers also market to different types of customers. Up where I grew up, it is mostly rural and many farms are 300+ acres. They sell a higher percentage of big AG tractors. Small tractors are 2nd (or 3rd+) and used to clean up around the farm stead or assist with pulling trailers or wagons while the big tractors are working. In suburban areas like I am in now, most tractors are small and spend most of their time landscaping. Dealers here sell few AG tractors as they are too big for the properties. Margins are larger on the big stuff, so they can sell fewer and still make payroll.