Hello Kitty's lack of a mouth is a deliberate design choice by her creators, and it has become one of her most distinctive features. While there is no official explanation for why Hello Kitty does not have a mouth, there are a few theories that have been proposed.
One theory is that Hello Kitty's lack of a mouth allows her to be more relatable and open to interpretation. By not having a specific facial expression or mouth shape, fans of Hello Kitty can project their own emotions and thoughts onto her character. This makes Hello Kitty a more universal character, and it allows people from different cultures and backgrounds to identify with her.
Another theory is that Hello Kitty's mouthlessness emphasizes her positive values of friendship, kindness, and love. Without a mouth, Hello Kitty is unable to speak negatively or say hurtful things, which reinforces her message of positivity and inclusivity.
The reason why Hello Kitty does not have a mouth remains a mystery. However, her lack of a mouth has become an important part of her character, and it has helped to make her one of the most recognizable and beloved characters in the world.