From Indy's first years all the way through the late 1980's, Indy was the one race that ALL the racers showed up for. To win Indy, you knew you had beaten the absolute best racers from all the states. From California, Oregon, Washington State all the way to Maine, Jersey, NC, SC, Florida and Texas. The entire North American "drag racing world" showed up for Indy. The same could not be said for any Pomona race or the Gators.
It's as Roger Gates said, qualifying was unreal and just to qualify for Indy meant you were one of the 16 best in the country and you didn't want to be one of the 44 cars that towed home without making a pass in Monday's eliminations.
Unfortunately, now a team can qualify #16 at Indy with nobody behind them in T/F or F/C. It's a different drag racing world now for many reasons. The folks that now think of Indy as just another race probably weren't around for it's glory days.