The premium is calculated on the extent and nature of the cover you want. A higher sum insured means a higher rate of premium. Similarly a higher risk will be charged a higher premium. An example of this is that an older person will have to pay a higher premium for health insurance for the same sum insured. Sometimes the risk is higher depending on the location of risks for example in motor insurance in areas where accidents are higher. So the premium will vary according to the nature and severity of the risk.
If I buy a policy and dont make a claim, it is a loss. So, why should I buy insurance?
General insurance is not meant to be for savings or investment returns. It is meant for protection. What you pay for is the protection against a risk. To approach it as something from which returns should be obtained is not the correct approach as there is a price to pay for protecting a property worth lakhs for a few hundred rupees.