I used to run 10km per day, and 20km twice a week, which is about 56 miles a week, or 2900 miles a year (with no days off). Definitely doable. Now I’m lucky if I run 10km a week.
I did 2200 miles last year and trained closer to 8min/mile. My half marathon time was ~1:27 or 6:41/mile pace on the San Francisco hilly course.
I learned through pain that stacking up miles is about patience, not pushing harder. Right before tapering, I was averaging 80miles / 10.5 hours per week for 4 weeks in a row. About 1.5 hours per day.
As a thought exercise, running avg 7min/mile (MUCH harder + higher injury risk!) would decrease daily time by 11 minutes. 6 min/mile average (~olympian level training pace) decrease daily time by 22 minutes.
If you want the miles, you can get them. But you have to wake up 2-3 hours before work and run every day. And don't drink too hard on any weekend, otherwise you can't get quality long run in. And don't run too fast, otherwise you get injured/sick. And don't build weekly mileage too fast either for the same reason.
How come I couldn't keep my peak 80mpw average and hit >4000mi last year? Well firstly I wasn't fit enough in Q1. And then I failed to adhere to the simple rules above 39 weeks in a row afterwards!
My Strava feed used to have a few people who averaged 100 mi/week, but the number has been dropping as age, work, and family sets in.