I'm not positive but I think it has to do with the implied "you". Don't dare can mean a completely different thing so it can't have the implied you and mean the same thing. Whereas do not dare can have the implied you and still mean the same thing. So the sentences "Do not dare, (insert something you can do)" and "Don't you dare, (insert something you can do)" mean the same thing. But without the you Don't you dare becomes Don't dare which means to not dare, not not to do something but instead to simply not dare.
Do not you dare. Weird