日本人はなぜ生魚を食べるようになったのか?
Why did Japanese people start eating raw fish?

日本は海に囲まれた島国で魚が豊富 + 仏教文化が根付いた為
Japan is an island nation surrounded by the sea,
and Because of the roots of Buddhist culture

日本に仏教が伝来すると、仏教の教義による殺生戒めに基づき、675年天武天皇が最初の 食肉禁止令を発布しました。
When Buddhism was introduced to Japan, in 675, Emperor Tenmu issued the first meat-eating ban based on the Buddhist commandment to kill life.
仏教が普及した10世紀ごろ、動物を殺して食すことはタブーにされ後1200年間続きます。
Around the 10th century, when Buddhism spread, killing and eating animals became taboo and continued for 1200 years.

稲作を営んできた古代の日本人には血の穢れを忌み嫌う観念があり、穢れがある食物を食べると神の怒りに触れると信じていました。
The ancient Japanese, who were engaged in rice farming, had an abhorrent notion of blood contamination, believing that eating contaminated food would provoke the wrath of the gods
その為肉食は仏教で禁じている殺傷を犯す行為とされましたが『魚』だけは海の恵としてありがたくいただく そして和食文化には魚が欠かせないものになっていきました。
Eating meat was regarded as an act of killing and was prohibited in Buddhism, but only "fish" is gratefully received as a blessing of the sea. Fish is an integral part of Japanese food culture.

刺身は元々漁師が船上料理として食べてましたが新鮮な生魚は手軽で美味しく栄養もある為普及していきました。
美味しく食べる為 酢、醤油、わさび、生姜など工夫され日本独自の食文化に定着していきます。
Sashimi was originally eaten by fishermen as an instant dish on board, but it has become popular because fresh raw fish is easy, delicious, and nutritious. Vinegar, soy sauce, wasabi, and ginger have been devised to make it even more delicious, and it has taken root in Japan's unique food culture.

海の恵をいただく為食事をはじめる前に必ず 『いただきます。」感謝してから食事をします。
命を頂く感謝もあり日本では残さず食べることがマナーとされるようになってます。 2023/4/30UP
To receive the blessings of the sea, be sure to "I'll enjoy having this. "It's become a manner to eat after thanking.
In Japan, it has become a manner to eat without leaving any leftovers.