The difference between short, medium and long haul. For the same number of hours, the short haul pilot has to fly a lot more sectors. It's hard work, and wears you down even more than the time zone changes of long haul.
As an example, the year I got my highest hours in the 767, I flew 219 sectors. A year or so prior to that, I'd flown 100 less hours, but 20 more sectors.
Highest hour year:
767, 219 sectors, averaging 3.5 hours
747, 82 sectors, averaging 9.0 hours
380, 70 sectors, averaging 12.1 hours
You can imagine what a year would look like if you just flew the east coast with sector averages around 1.3 hours. It's why MEL-SYD-BNE is called the monorail.