Because Indianapolis is the biggest and most important race in the world. If you claim a world championship--as does Formula One--then that "world championship" should properly include the biggest race in the world.
But even leaving that aside, if you are a race car driver, you should race Indy because it's the best. The same goes for Le Mans. Race car drivers should drive there.
“Indianapolis” is the biggest race in the world? That is an opinion. But I think you mean is the Indianapolis 500 race for “Indy” cars on Memorial Day weekend.
F1 cars and the F1 series has never had anything to do with the Indianapolis 500. Different cars; different series completely.
‘Indy is the best”. Best what? Not track.
It has history - for Indy cars - but that is about it. For Nascar, Rocky is more important historically.
Le Mans is an endurance race. Not a drivers race. It goes for 24 hours and lots of changes of drivers. It is all about engineering.
“you should race Indy because it’s the best.”
LOL. Danica, the Venezuelan slut, and Sarah!! LOL. If it is so good why do all the open wheel drivers drive Nascar! LOL
Indy WAS the big race. NO MORE. Done and gone.