Farm hands were close to 30% of the jobs in the U.S. before the combustion engine - now they're <1% of the jobs. Entire towns consisted of farm hand jobs, and people migrated solely for them, so the job itself was more important than anything we have today.
Whereas farm hands and secretaries have transformed, and were not so densely localized. (And farm hands are still needed, large industrialized farms are still rather labor intensive, just more area can be successfully managed by the same sized staff + a lot more capital/machinery.)