There can be many reasons to why you have limited dream control. Some of the common reasons are strong emotions, especially frustration, often caused by your inability to control the dream, which can turn into a vicious cycle.

If you have any doubt whatsoever whether you can do it, then you can't.

You may also have become so used to not being able to control your dreams that your dream control problems are keeping themselves up.

To find out just why you are struggling with control, you should ask yourself some questions. What are your thoughts and feelings when you try and fail dream control? What are your thoughts when you find yourself unable to? Are you bound by "dream logic" during the lucid dreams where you have to finish the plot?

I hope this helps some.