If your company has high attribution. This piece of information will shed light to your search of reasons. 
People leave bad bosses. 68% people left their jobs are due to their bosses. According to Saratoga Research Report (Authored by Leign Branham) on why people leave their jobs.
They have interviewed and studied 20000 employees who left their jobs. Below is the listing of those reasons:
Too few growth and advancement opportunities 16%
Lack of support by and respect from supervisor 13%
Job Duties Boring and unchallenging 11%
Lack of leadership skills by supervisor 9%
Not recognize for my contribution 4%
Display favoritism 4%
Poor supervisor-employee relations 3%
Training 3%
Incompetent supervisor 2%
Poor senior leadership 2%
Supervisor lack technical skills 1%
Leign Branham has proposal seven strategies to counter the outflow of employees. He has suggested many practical steps in his book "7 Hidden Reasons Employee Leaves". Among others, 
To Match Expectations with Reality
Select the Right Talent for the Job
To Provide Coaching and Feedback
To Provide Career Advancement and Growth Opportunities
To Make Employees Feel Valued and Recognize
To Reduce Stress from Work-Life Imbalance and Overwork
To Inspire and Confidence in Senior Leaders
If you follow his suggestions, your company may well be the employee of choice one day.