I can't say outside of some facebook posts that I saw from COTA and Indy that I saw a single word about the race. About 2 months ago, COTA swooped into the McNay Art Museum and then New Braunfels City Hall for a picture op, they seemed to be at each stop for maybe 30 minutes. Do something at those. Make a big announcement splash in each city. Invite people out to come sit in the static display car and get their picture taken. Something. Anything.
What promotions did you see? Obviously my experience varied greatly from yours, so that would certainly point to a marketing issue.
Its more than just the Indycar fan. Those are gonna go no matter what. Marketing them is obviously wasted money. It's marketing to the average person on the street and convincing them to go and drop some change. I'm not sure what COTA would need to do - but if they don't do something, they will run off yet another series.
Cost:
Indy for Sunday only was $65 for general admission. Parking in Lot T, $30 (if they remember to charge you.
TMS Sunday only, $30 right now on Ticketmaster, parking free.
Parking is MUCH better at TMS. Granted you are stuck in a single seat at TMS, but you can bring a cooler in, that alone is worth a shit ton of money since you can pack that fucker with hard shit. COTA - no coolers, maybe no drinks depending on which person "checks" your stuff".
As to how many fans showed up, we may never see a real number. Our hill at Turn 1 was decently full, but the Turn 12 and Turn 1 grandstands were bleak. There were people in the grass by the esses, but I doubt (I couldn't see but I'm guessing) that there were many fans past that to Turn 11 and back to Turn 12 because COTA didn't run shuttles down there like they do for F1. Of course, without fans there, no need to. And we can look at the parking lots and see what's up. Lot T was full, but N was turned into camping (almost completely empty) and I'm almost certain they didn't use L or M at all, not to mention Q off of 812. And then they turned C into a .25 USAC Midget track.