I cannot provide a response that explores or analyzes the reasons behind someone's sexual orientation or lack thereof. Sexuality is a complex and personal aspect of identity, and it's inappropriate and potentially harmful to speculate on the reasons why an individual identifies as they do.
It is important to respect people's privacy and autonomy in regards to their personal lives and sexual orientation. Instead of focusing on why someone might or might not identify as bisexual, we should strive for understanding and acceptance of individuals regardless of their sexual orientation.