There could be several reasons why your KDP book is still in review. Some possible reasons include:
1. KDP may be experiencing a high volume of book submissions, leading to delays in the review process.
2. Your book may contain content that violates KDP's content guidelines, leading to a more thorough review.
3. There may be technical issues or errors with your book file that need to be addressed before it can be approved.
4. KDP may be conducting a random quality check on your book to ensure it meets their publishing standards.
If your book has been in review for an extended period of time, you may want to contact KDP customer support for more information on the status of your submission.