Because of his itch hands, that's all. It is a good practice for certain people, so don't stop them from doing that. There always some people hands itch, not a bad thing, not at all.

On the other hand, let db do the sort isnot always the solution. For example order by doe snot play with things like limit in some db implementation. In those cases, you are forced to do the order by yourself. Of course nested query is also a solution. Voila.