As someone who has worked with several of these companies, there are several things that go into the contracts on these events. #1 your bigger stadiums will not rent to 1 promoter for the first few days, then another promoter for the last few days. This is basically damage concerns. Also a group like Feld will not set up a 2nd event because there is no way they could sell out a large facility. THey will also not take any injury risk. They have there business model and it works.
#2 many of the big contracts have non compete clauses. For example Feld has a 2 or 3 month clause in there contract. No motor sports events may be held 2 months prior to there event or 2 months after there event.
#3 Daily cost- as stupid as it may sound, in many venues large groups like feld will start removing the dirt that night. They will have everything removed within 24 to 36 hours of the event ending. Every building has a daily cost. Many feld events happen on back to back weekends (monster Jam 1 weekend, motocross the next weekend). They will truck all of the dirt out by the end of the day sunday. Then haul it all back in starting on wed. It is cheaper to haul the dirt out, then right back in than it is to leave it in the stadium all week long.

The cheepest way to race indoors is on concrete. That will not happen in Indy, because the field is permante. I know it sounds stupid, but under all of that dirt is 2 to 3 layers of plywood. Then plastic, then the actual field.