Like if new England had the most entries, they'd hold it at Lime Rock?!

If a weekend is $58K, can you imagine how much the rental for the entire event would be!? But that's irrelevant, the track just isn't appropriate. Too small, too short, no paddock space. That's the issue, not all regions have an appropriate track.

Further, some regions run more races, so they will naturally have more entries. Season is longer in Florida, so maybe THEY'LL have the most entries.

Bottom line is that there are only a few tracks in America that can handle an event of the size of the runoffs. Road America, Mid Ohio, Road Atlanta, Miller (yech) mayyyybe the Glen, and Daytona. I don't think that Sears (Infineon) is big enough, and Laguna is possibly big enough but there are so many restrictions there, I'm not sure it's feasible to deal with those. I've never been to Willow...the west coast guys can correct me on all this of course.
I think you could throw out Daytona, the California tracks and Watkins Glen as being "too far" for most ...unless the BoD has decided the Runoffs will move around every year visiting east then west then middle, and they will live with the attendance varying .