The Reason

Japanese people often say "I studied English from high school to college for more than 10 years and still I cannot speak English." This leads to the conclusion "I may not have linguistic talent or I am not linguistically minded." But wait a moment. Then why can you speak Japanese?
In my view, Japanese people in general are poor English speaker just because they study English only for a short time. Of course ten years is not short. But they have to say "I have been studying English ON AND OFF for ten years." English level is simply a function of the time you are exposed to English. Say, If you stay in the USA for one year, you are exposed to an English environment for 365x24= 8760 hours. If you exclude your sleeping time of 8 hours a day, still it is more than 5000 hours. You studied English for 10 years but have you studied 500 hours a year? Have you studied more than 1.5 hours a day constantly everyday with no exception like "Oh I drank too much" or "I don't feel like studying today"? I doubt it. Before starting to doubt your method of studying, doubt your effort. There are many fishy books that boast "３ヶ月でぺらぺら(Speak fluent in 3 months)" or "中学英語の復習でぺらぺら(Speak fluent by just reviewing high-school English)". If you realize that you haven't studied English for a long enough time, you will not fall for those catchy promotional phrases. Do not buy expensive books or English materials. All you have to do is go buy an English novel now and read it for 3 hours a day. After you finish it, buy another book and read it. If you can continue this for a year, you will make a remarkable progress. But please be noted that it only covers a little more than 1/5 of the hours staying in US for a single year. This is a simple arithmetic. It's not true that you are not linguistically minded, if you may not be arithmetically minded.
The photo was taken in Zurich Switzerland. Some shops in European cities have their original sign board like in this picture.