There could be a variety of reasons why a boy doesn't reply to messages after confessing, and here are some possible explanations::
The guy hasn't made a decision yet: it may take time for the guy to think about and evaluate his feelings for you and whether he's ready to enter into a relationship. Therefore, his non-return message may mean that he is considering it and has not yet made a decision.
Guys don't feel the same way about you: If guys don't feel the same way about you, they may find it difficult to reply to your confession. He may want to express his feelings in a way that doesn't hurt you, so he chooses not to reply.
Guys don't know how to respond: Guys may choose not to respond because they don't know how to respond to your confession. He may be surprised or confused and don't know how to express his feelings.
Guy busy: Sometimes guy doesn't reply to messages because he's busy and doesn't have the time or attention to respond to your messages.
Guys have negative feelings about you: If a guy feels uncomfortable with your confession or has some negative feelings, he may choose not to reply. It could be because he doesn't feel able to handle the feelings, or he doesn't want you to misinterpret his response.
Whatever the reason for the boy's refusal to reply messages, it is important to respect his decision and give him some time and space to deal with his emotional issues. At the same time, maintain your dignity and self-confidence and do not rely too much on his response or allow yourself to fall into negative emotions.