The snare is less than 4 feet away from the drummers head. How on earth can they not hear that? (Without running it through the PA.) Large stages with the band spread out? Yea, they will need monitors, but the drummer should have an easier time hearing himself with everyone else pulled away. On the other hand, it's always been recommended that if the band is normally packed tight when playing, they should also pack tight especially on a large stage so what they hear is closer to normal.
At one outdoor gig where I was playing keys, the drummer's monitor was aimed my direction and the kick was so loud (outdoors) at 12 feet, that I asked the monitor engineer to do something. It was totally drowning out my monitor that was a mere 5 feet from my head. (And no, I didn't want my monitor turned up. It was really loud enough and the drummer normally played without a monitor. It was all the engineers fault. There was no call for that much monitor from any point onstage.)