Well, I am not going to answer your question exactly as you posed it for one simple reason. The reason is this--you can be invisible. All you need is to know how. I know how to be invisible, however, due to some bad experiences I've had with people I taught the skills of invisibility to, I decided long ago never to teach anyone the secrets of invisibility again. So perhaps I can answer your question. Why can't you be invisible? Because I refuse to tell you how.
But logically in most minds this will lead to the follow up question, "Why won't you tell anyone how to be invisible?" It's because once there were people in my life who were capable of being invisible it made my life much more difficult. My dominance in hide and seek definitely nose-dived and I was feeling guilty every time I saw a report of a robbery on the news in which I knew the robber was someone who was abusing his or her power of invisibility. Not to mention...well, perhaps I needn't go into all the details.
The main point is that I needed to end up wiping their memories and recreating history using the alternate reality key on my...ha, pardon me. The story of the alt key isn't what you asked about. I shall answer that one another time.