"A computer is a general-purpose machine. A tractor is not."

I mean, a tractor can't do everything, but I'd be hard pressed to find something in the farmers tool box that can get a wide ranges of tasks completed.

Pretty much all farm tasks require it: Drilling, discing, spraying, cutting...not to mention pulling wagons, goods to market, etc etc.

Exactly, the tractor was the general purpose machine for agriculture and all of the land management tasks that were tied up with that and modern people forget that agriculture used to be 60% of employment. If you broaden that to the motor then it really is a general purpose machine for all physical labour, which is something a computer is not capable of doing.