That's because when we first studied electricity, people knew that there were two kinds of charges, but they didn't know which kind of movement, so the direction of positive charge directional movement was the direction of current.
But later, through further research, it was found that in metal conductors, negative charges (free electrons) move directionally, while positive charges do not. But it was previously stipulated that all documents should be changed if they were changed. Also, in acid-base salt solution, positive and negative charges (positive and negative ions) can move directionally, so they still follow the original law.
Moreover, it should be noted that positive charges cannot move directionally, not without movement, but irregularly in a small range (vibration).
The positive charge cannot move directionally because the nucleus is positively charged. If the nucleus can move directionally, then the metal conductor is not fixed.
The reason why positive charges move (irregularly in a small range) is that matter is composed of molecules, while the molecules of metal conductors are monoatomic molecules, that is, an atom is a molecule, and the molecules are constantly moving irregularly. The activity space of solid molecules is very small, and they can only move irregularly in a small range.