Why is livery insurance so hard to get and so expensive?

I am in the process of starting up a shuttle transportation service. However, one of the biggest problems I am having is getting the insurance needed. This is a "for hire" shuttle service, meaning customers pay a fee to ride on my 15 person vans. Almost every insurance company I called said they don't... show more I am in the process of starting up a shuttle transportation service. However, one of the biggest problems I am having is getting the insurance needed. This is a "for hire" shuttle service, meaning customers pay a fee to ride on my 15 person vans. Almost every insurance company I called said they don't offer this type of insurance, and the one that did quoted me $8,000 to $10,000 per year!! What's the deal here? What type of insurance does the famous supershuttle company have? Does anyone know how to go about getting this insurance??