it would equate to the other half paying over $50 per month in fees, 2 overdrafts per month.
That number is definitely believable. I was a bank teller in college and there were a good number of customers that seemed to be perpetually overdrawn.
I can't remember if this has changed or not, but banks would charge you for each item that hit after you went negative and they would have the largest debits hit your account first so they could maximize the number of items that hit after you go negative. So if your balance is $10 and you swipe your card for $1, $1, $1 then $10, they made sure that $10 item hit your account first so they could charge you three fees.
I still work at a bank but far removed from branch life so I'm not sure if the CFPB has put an end to this.