The US has inexpensive MRIs as well. This nationwide chain provides MRIs as low as $335 depending on the state. http://a2zimaging.com/ No insurance accepted, no payment plans. Those cost money. Just charges the cost.
Insurance works great for catastrophic things, just like car insurance and then it clearly makes sense to make it universal. If you could only buy gas through your car insurance--who occasionally would decide you drive too much and not cover this months' gas--you can bet prices would go sky high.