1 They are not emotional
People who use emojis are usually more emotional and emotionally expressive than those who don't. People who don't use emojis might be less emotional than those who do. (See 20 Signs That You Are Emotionally Sensitive)
2 They don't trust people easily
According to psychologists, people who don't trust others easily might find it hard to use emojis since they make them feel exposed. Emojis allow people to express themselves and so those with trust problems might not feel comfortable exposing themselves using emojis.
3 They are cold
People who are cold or who don't show a lot emotions in real life might never use emojis in their chats. This habit is just a reflection of their true personalities.
4 They are insensitive
People who are not emotionally sensitive might use few or almost no emojis while chatting. In such a case, those people don't get too emotional while messaging and so they don't feel like using emojis.
5 They have less empathy
People who don't have high levels of empathy might not use emojis while chatting. Emojis in many cases are used as a tool to empathize with others and confirm their feelings.
6 To seem serious
Some people don't use emojis in order to seem more serious. Those people might want to give the impression to others that they are serious people.
7 They have high levels of testosterone
High levels of testosterone can result in a lower use of emojis. High testosterone levels can make people less friendly and emotional. (See How does it feel like to have high levels of testosterone?)
8 To seem masculine
Some men don't use emojis because they consider them feminine. Those men might never use emojis in order to appear masculine and strong.
9 They consider them childish
Some people don't use emojis because they consider them childish. Some people might never use emojis in order to seem more mature.