I can't speak to bike races per se, but I am involved in organizing a different kind of event, and liability insurance is a huge PITA, and is expensive. And we have rigorously worded waivers.
One thing that a race like this has to contend with is that an injury could happen in any of a number of states, so jurisdiction becomes a problem. Looking at the TABR waiver, it doesn't have any language to the effect of "any disputes arising from this agreement will be adjudicated in XX county of YY state." Which seems like an oversight, now that I think about it.