Why can't iphone information be marked unread?

How to mark unread Apple SMS is only useful for some mobile phones? Clicking the menu button of SMS will change the message to unread, but not all mobile phones have it. It should be noted that this function only applies to messages in inbox and my folder, but not to messages in outbox and draft box. The steps of marking unread SMS on iPhone as read are as follows: First, enter the information interface of iPhone, and the unread SMS will be displayed first. Click the edit button in the upper left corner to enter the editing interface. Find the "Read" button in the lower left corner and click it. After clicking this button, all unread messages will become read.