Tractors replaced farm hands, not farmers. Software developers are farm hands.

Why not both.

An absolutely massive numbers of farmers were replaced too. Farm management was rather grueling in the early 1900s. Farmers that embraced mechanization were able to buy up surrounding farms that didn't and grew in size. As the equipment got better the amount of work per acre farmed dropped so farms expanded with more acreage. Farmers and hands dropped in number.