Are you in Japan and subject to Japanese tax law?
Yes; I work full-time in Tokyo and all my income is here. If only I made enough ($82,400 is the threshold now) for the IRS to get interested in me!
I think most banks tax interest on savings before you receive it. On securities trades you can choose to report it yourself. Also, for national tax your employer will figure out what you owe and make year-end adjustments before paying you your December salary. And there are very few opportunities for deductions for the average person, so many people don't have to do tax returns at all.
Company-matched 401(k)-like investments are also very rare, so the average person just stashes their savings in the bank every month. I'd love to see them stop taxing those meager returns.