WHY DOES THE CONFUCIAN WORK ETHIC CONTRIBUTE TO WORK ADDICTION IN JAPAN?

It does not. Definitely not. The various concepts in the philosophy have been a useful set of tools for the rulers to manipulate and control their subjects with. Full stop. When I was younger, I hated it because I felt as if I were being suffocated by it.

I am not sure if the Japanese in general are addicted to work, but I do think Japanese work ethic was extensively influenced by Confucian teachings of faithfulness and loyalty in particular. It is true that their loyalty to their companies is amazingly strong, which I believe greatly contributed to their production of world-leading quality items in a variety of fields (in addition to their ingenuity and dexterity).

Although the Japanese are not necessarily aware of Confucianism as the basis for their ethical standard of 仁 benevolence; 義　Righteousness; 礼　courtesy; 孝　piety; 忠　faithfulness / loyalty; and 中庸 moderate / balanced, I do believe that both Buddhism and Confucianism, introduced to Japan approx 1,500 years ago, had a great impact in the formation of characteristics of the Japanese today.

BTW, personally, I am more interested in the fact that why Japanese would never accept Christianity No Matter What!! Not to mention, both Buddhism and Confucianism have a lot to do with this. But I shut up my mouth. This is obviously outside your question.