ime: Lack of time is the most related reason for not delegating. It assumes that charging someone else takes more time than doing the activity themselves. Exceptionally when limitations are tight, you may be more likely to move up your sleeves and do the action yourself.
Identity: Over the last few years, you have put in your area of expertise and your professional skills. New leaders often have their identity and sense of value at the office related to being influential individual contributors.
Emotional attachment: Many people are too emotionally invested in the activity to give it to someone else. For instance, you already have an idea in your mind of the final product, and you do not like someone else getting it differently.