Open Question: About construction insurance and bond.?

I live in Oregon and have to carry $300,000 worth of insurance and a $20,000 bond. The insurance is going to cost around $60. a month, however the bond will run me $7,000 a year. Which I think is ridiculous. a $20,000 bond that, at years end I will have paid nearly half of its total value. Maybe I don't have the info right. Isn't a bond basically like insurance, but it covers damages more quickly to help assure the consumer that, if all went wrong, it would be taken care of. If this is so, why do contractors have to carry insurance and the bond, if they are basically the same, why isn't the $300,000 insurance coverage enough. I realize that the bond may only cover actual physical damages caused by the contractor, so in this case one would still need coverage for all the vast possibilities that could happen outside this, and damages that may exceed $20,000. What I'm not understanding is, why can't I just pay for insurance that will cover every aspect of that particular business. And what if I never had to use the bond. Do I still have to keep paying for it every year. The math does not add up to me. I dont agree with all the tactics of insurance companies, but I understand how it works, I can actually see and understand the mathematics behind it, but the bonds I don't. That's an awful lot of money to be flushing if you never had an accident. I'm sure there's a few things I dont have right and/or that are just plain missing. that's why I'm asking. And one more thing. Can one purchase insurance and bond coverage from out of state firms? thanks for your time and responce