How does the Indy Racing League IRL stay in business?

I’m asking this from the standpoint of watching the race at Texas yesterday and nearly being blinded by the sun reflecting off 90% of the seats which were empty. The same thing is prevelant at Nascar Busch series and Craftsman truck series races. I relaize that the Nascar stuff may have the resources of Nascar behind them but what about the IRL? It must cost a ton of money to rent out the speedways every week, so what gives?