Why are the Japanese not keen to stop their practice of slaughtering dolphins?

Not exactly the right answer, but Japanese kill whales because during the second world war the US bombed a large number of ports and other places of interest in Japan. Japanese therefore had a lot more trouble getting food. Whaling provided food for a whole town for quite a long time and helped Japanese towns survive.

This way of life has prevailed in Japan through older people and their close associates. Pretty much any Japanese person you meet will not be a supporter of whaling, and such a view has shortened into small groups of people. It is therefore not the case that Japanese want to kill all the world's dolphins and whales, but that some people still hunt because of a prevailing and outdated way of life.

I don't have any sources for this because I forgot where I learnt it. Maybe it was LOTE...