Because we are still farmers who need to wake up at 6AM in the morning?
Cows also don't care about property lines :)
But I worked blue collar after that, my job 7:30 to 5:00, or 7:30 to 8:00 on long days.
Even in my current white collar job, that habit has stuck, and I have been working 7:30 AM to 4:30 AM for the last thirty five years, mostly to avoid the bulk of the commute.
So yes, there are millions of jobs across this country where people arrive at work, and punch in on a clock, at 7:00 AM every morning.
I start work at an office starting around 8:30-9:00 and I wake up at 6AM. Not quite sure what that time has to do with farmers.
My (late) grandparent were farmers: they only cared about the time on Sundays to make sure they weren't late for Church services. Otherwise the the cows needed milking when they needed milking (which I helped with when I visited them).