Most event directors, college coaches, athletic directors and/or staff do not care that much about things like clean air, emissions or the environment.
The sad truth is most people are the same.
Inefficient gas powered vehicles are ubiquitous. EPA standards allow things like ATVs, Gators and dirt motorcycles to spew far more toxic and damaging emissions into the air than cars or trucks. Gasoline is inexpensive and the full cost of using it is not considered by most.
There are not that many electric vehicles out there. Most golf carts are set up to be too slow to lead decent runnners.
If pressed on this issue, the event organizers would likely say the exhaust is the same for all the leaders.
Also remember pre nats are in Indiana. I have lived there and it is not the most environmentally aware state. Surprising they do not lead the race with a diesel tractor or a Hummer.
IN is a pretty conservative place. Check out Indiana Governor (and Trump running mate Mike Pence's) abysmal views on environmental issues.
I have been in some races on USFS dirt roads where the lead vehicle was an ATV, The noise and exhaust were awful. The lead pack spent the first few miles trying to yell at the driver to give us more space.
They could find some respectable mountain bikers to lead these events. Yes you can film from a bike. But would spectators respect people on bikes?
Could the f-- a-- guys they pick to lead a race even ride a bike faster than 15 mph (4 min mile pace)??
I have volunteered to lead some local road races on a bicycle. Easy and fun to do.