I can drive a car but I guarantee you no NASCAR team would want me behind the wheel. If I can drive safely and get from point A to point B, why shouldn't I be able to drive for a team?
Easy answer - because it's pretty much guaranteed that I would wreck, and 100% guaranteed that I would come in last if I could even finish. Plus, who in the heck would want to watch me race (other than for the laughs)?
Similarly, did you know that elements of your website can not only be wrecking your chances for good search engine ranking but can also be driving visitors away?