You should be aware that the Equine Liability Act does not prevent someone who can prove *negligence* from collecting damages. Normal, unpredicatable horse behavior, yes, but if you forget to tighten the girth or don't fasten a helmet you can still be held liable for resulting damage or injuries.
Folks who conduct risky businesses without insurance are usually people without assets. No one will sue them because there's nothing to gain. If you (or a parent or guardian) have assets - houses, cars, savings accounts; it would be extremely unwise to conduct a business without liability insurance.