Are you sure you were watching the same race that I was? Everyone on the lead lap came in on the last stop. The 7 or so cars that came out in front of JPM and Biff all took 2 tires. Biff and JPM took 4.
Indy is not a track that favors handling. If this was Texas, Charlotte, Chicagoland, or any other cookie-cutter 1.5 mile oval, 4 tires would have been a great call with 20 laps to go.
But Indy is very difficult to pass at, and a car that takes 2 tires can easily hold off a car that takes 4 tires. 20 laps to pass 8 cars is not enough time at Indy. Assuming the race stayed green, you've have to pass more than 2 cars a lap to make up that track position. That's a tall order for one-groove Indy.