I think it’s because you have a negative view about assertiveness or commanding attention from others. Maybe you equate powerful speaking with being a tyrant. Or you are just generally afraid of your own potential in life. Afraid to acquire what you desire, such as a romantic partner, or appraisal from people you admire. Because you don’t feel like you can handle positive outcomes, or that you even deserve them at all. Because you have these restrictions that you hold on to, almost like an alarm system in your brain, the only way to get past that alarm system is to speak quietly to not set it off. You need to lessen the sensitivity of the alarm system. I think you need to accept speaking loudly and powerfully, and know that you can be assertive while also being a responsible and empathetic leader for the people around you. Also, accept and become more passionate about your potential in life.