But I was under the impression from other comments farmers could fix anything themself, so why can't they fix Kubota machines?
No one said farmers are not able to repair other brands.
The point is not all dealers/part suppliers are within a geographically reasonable distance. Think in hundreds and hundreds of miles or states away. Not just the other side of town.
John Deere on the other hand has rather dense distribution by comparison.
Just look at the huge list of implements here: https://www.kubotausa.com/products/tractors/utility/m4-serie...
So great, you bought a Kubota. Your nearest Kubota dealer can end up being 400 miles from you. They don't ship these things, you come buy and pick them up.