People often say that Japanese people are collectivist. That is, they value acting together and acting for others rather than for individuals.
There are many reasons, but one of them is said to be the fact that the Japanese have been cultivating rice since ancient times (note 1). In rice farming, there are many jobs that must be done together, such as transplanting rice and harvesting. In addition, if you want to grow a lot of rice and grow it well, you must manage the water used for rice growing in the entire region, not just your own fields.
During thousands of years of rice farming, perhaps in Japanese society, people (みんな) have become a very important standard.
(note 1) 稲作: growing rice, making rice.