Not so strange actually. Sure, seen superficially, it seems that double negatives negate each other but that doesn't fit the empirical data. Many languages do this in their standard variety and English does it in many local, social and historical varieties. I think Shakespeare did it too.

Spanish for example has "sin nada", literally "without nothing" but meaning "with nothing"/ "without anything".

So the linguistic consensus is that the negative is expressed more than once. Depending on the language this might be optional or not. Slavic languages have a negative prefix "ne-" on verbs and this is obligatory if a negative word (like never, nobody,...) is used in the sentence.