Farming is one of the hardest jobs out there. You need to effectively run your own business on fine margins often relying on government subsidies which can change over time, with a lot of risk due to crop failures/livestock disease (culling can be necessary for chickens due to bird flu etc). It requires hard manual labour running the farm with physical risk to you if you work with livestock. Cows don't care if you get sick, they still need cared for no matter what, there isn't much space for holidays or illness. This isn't to mention the few times of the year the tractors are used as you describe, but most tractors aren't this fancy, and how would you like to spend all day every day for a time working the land with the tractor from sunrise to sunset?

Most farm jobs are not sitting in the tractor all day. There are only a few farms in the world where a tractor has someone sitting in it all day every day. Most farms the tractors are used for 80 hours a week just a couple weeks per year (planting and harvest time). The rest of the time the tractors sit in the shed. There is a lot of non-tractor jobs farmers do. Many of the farms where the tractor is used full time every day the tractor is just pulling the harvest wagon and the crops are harvested by hand - one person drives the tractor while 30 walk behind it harvesting the crops.

The autonomous tractors are for use in fields where there are no other humans (at least so far)