This is very true. The legislation came into place around 2010, and the latest numbers for Japan suggest that about 2% to 4% of the eligible men actually take it. The main problem is that if you take leave, this is perceived as curtains for your career, or as detrimental to it.
However, there are signs that some change is happening. If you look at Korea, about five years ago about 2% of the eligible men took it. That has gone up to over 5%. What's more, once Korean men decide to take the leave, they actually take it for a long time. On average, their period of leave is about eight months, only a little bit shorter than that for women, so there are some encouraging signs there. I won't say that this is a major breakthrough, but if it can help bring about a shift in gender expectations in this area, which could do wonders in the long run.