Put your thinking cap on for a moment, please.
Imagine, for a moment, that the first bike of the group to go into that corner of that meticulously clean track, had its engine explode.
What do you think is going to happen to the group of riders immediately following behind?
YES they clean the track. NO if the engine explosion happens in your session, that's not going to help you. YES they have belly pans. NO that will not stop oil from getting out in the event of a catastrophic engine explosion. YES they have track marshals who have a "debris" flag in their possession to warn riders of track contamination. NO this is not going to help the riders immediately following the one with the exploded engine ... the marshals won't have had time to figure out what is going on yet, and even at the best of times, once you pass one flag station it is a finite distance to the next one, and if the engine explosion happens between those flag stations and you happen to be between those flag stations behind the bike with the engine explosion, then even if the corner workers miraculously were able to put out debris flags the instant the engine explosion happens (which cannot happen in reality) you are STILL going to be riding through oil.
I've been that bike following someone who had an engine grenade. Happened at the entrance to the Carousel at Grand Bend. Fortunately, I was close enough to see the telltale signs half a second before the engine went boom, and used that half second to duck to the inside edge of the track, inside the path where the oil was going down. The rider behind me didn't see that, and went down.