I think i understand OP's question. @Santhosh sivan accomodation and catering establishments (i.e. hotels and restaurants you're trying to get employment at) are desperately in the red at the moment. Far from hiring new personnel most of hotels and restaurants are facing a tough choice between bankruptcy and bitter layoffs . It has nothing to do with your diploma. Try again when the world gets back in order.
What is a diploma candidate? Foreigners can't be hired unless they satisfy visa requirements.
You are married to a Japanese and have a spousal visa or permanent resident status.
You are not married to Japanese and you have a PR status.
You have a work visa, which usually means you have a 4-year college degree. (many years of related work experience can substitute for the degree)
You are a dependent of a Japanese and have a dependent visa.
You are on a working holiday visa. (this depends on your country and its arrangement with Japan)