I blame the promoter(s).

There are tons of ways to involve local businesses and bring out local residents to a bike race. Stream of consciousness here but:

1) Put together a coupon book that feature retailers/restaurants/whatever along the race route and in the area. 5% off this, free dessert that. Distribute coupon book to racers in their race packets, distribute to locals both at the establishments ("Hey, thanks for visiting Fat Al's BBQ. Here's a coupon book with a bunch of discounts for this Saturday, and there's free entertainment too. Yeah. Bunch of adults riding bikes in spandex. Should be a hoot!"), door to door (if it's feasible), or even drop a mailing a week or so to local residents (within the zip code or surrounding zip codes).
2) Do something other than a bike race. Are there local gyms? Get them out to host a free fitness class. Bring out a moon bounce for the kids.
3) Raffles and giveaways.

there are tons more ideas but this is a gist.