Someone asked about the racing line at Indianapolis on Quora. The snake pattern looks nothing like a conventional racing line. The answer below covers it. It is about drafting. But why is drafting the biggest factor? It is partly a result of restrictions to slow the cars down. If the cars had the aero/horsepower to make the best use of the track, there wouldn't be this snake racing line. The faster way around the track would just naturally be a conventional racing line. And anyone drooping down to the very bottom way before even the pit wall starts, would get passed by someone making a conventional corner exit.
At Indy, drafting and passing is pretty essential. A basic defensive technique is to deny the inside line to drivers behind you. By driving in the middle of the track, passing drivers would have to go so far to the inside of the opponent that their turning ability would be greatly compromised if they couldn't completely clear the opponent before corner entry.
This manifests itself in the goofy snake pattern you see. Even drivers who aren't defending follow the line because they want to be in the aero wake for fuel savings