Translation:Excuse me, is the bathroom here?
"Is there a bathroom here?" in Chinese is "有洗手间这里吗?" or using the alternative way of asking "有没有洗手间这里?"
"Is there a bathroom here" implies you don't know if there is one. "Is the bathroom here" implies you know there is a bathroom somewhere around but you want to verify its location.
For the same reason your question is wrong. In English, we invert the subject and the verb (the main verb or the helping verb, depending) when asking a question.
Your sentence should be "Why is 'Excuse me, the bathroom is here?' not accepted?", or "Why isn't 'Excuse me, the bathroom is here?' accepted?"
It wouldn't be literal. I believe you could say "洗手间在这个方向吗？"
(It would be helpful if a native Chinese speaker could confirm this. I would say it, and I know I'd be understood, but I'm not sure if it's entirely natural-sounding, or if there's a better way to ask the question.)