Remember, everytime an airlines "gives" you miles, they are holding on to you as a future customer. It takes a lot of miles to get a free ticket and you spend a lot of money to get that free ticket.
If giving extra miles to "customers" was a problem, there would be no FF programs.
They know exactly what they are doing - keeping us as loyal customers to their particular airline.
Consider that many of the promotions they run for 100 or 200 miles is to make sure you are returning to their websites.
Also remember that if a plane is full in first and business with paying passangers, the flight is paid for at that point.