that's not exactly the best assessment of the kaplan tests or perhaps any test company tests.
The tests provided by the test companies give you a generous score is because their tests are harder than the practice aamc tests that are available. due to the difficulty they give a more generous scoring system to compensate. if you've looked at the aamc tests and see their correlation between raw scores and the 15point scale.. that's fixed. unlike the practice aamc tests, the tests provided by test companies ( i can speak for kaplan and princeton) is that their scores will vary depending on the number of people taking the tests and the difficulty.
best of luck !