This is a standard requirement and the exam is paid for by the insurance company.
The insurance company requires a physical exam to determine your current health and see if you have any health issues, or you lied about any health-related problems on the application for coverage.
The reason you may need a new exam is because your health may have changed since your last physical examination.
The exam helps the insurance company determine your health, review any health problems, and make a calculation as to your longevity - how long you are expected to live. That way, they can decide if they want to insure you for life insurance, how much coverage to offer you, and what they should charge for your life insurance.
In addition, there are some insurance companies that offer life insurance plans without any physical exam required, just some health questions. Here's how you can learn about term life insurance with no exam required.