I'm not quite sure why companies write mission statements, but I assume it is in order to commit their employees to some sort of common goal. Logic dictates that the statement should be concise and easy to understand, so that the average employee can grasp what the company's goal actually is, e.g.
[Company] aims to make the world's best pancakes!
Should you ever be asked what your job is or why someone should choose your company before another, there's your answer.
Unfortunately, because of their strategic nature, mission statements are often considered top priority and as such, they are developed and written by upper management. This leads to statements such as
[Company] continuously keeps the company product portfolio modernized and updated in order to be our customers' first choice, and R&D is the main contributor to our overall vision of becoming the Leading technology supplier in [market segment], with special focus on [buzzword 1] and [buzzword 2]".
That's quite a mouthful. You can almost smell the cold sweat as the committee tries to cover all the bases just in case some C-level manager should decide to have a look and check if the lower echelons have internalized what the company really stands for.