Some people get angry when others don't reply because they feel ignored. These days, everyone expects fast replies, so when someone doesn't answer, it can feel like they're not important or being rejected. This is especially true if it's a close friend or family member. It can really hurt their feelings.

Another reason is that people worry something might be wrong. If someone usually replies quickly and suddenly doesn't, it can make you anxious. You might think they're upset with you or maybe something bad happened. This worry can make people feel angry or stressed.

Some people think not replying is just rude. They see it as bad manners, like the other person doesn't care about them or the relationship. In some cultures, replying quickly is a sign of respect, so not doing it can be seen as disrespectful.