Please don't take this as an insult if you did indeed mean what I suggest, but since you say you put them in your "Addons folder in your WoW directory", do you mean WoW (or whatever you named that folder)\Interface\Addons or WoW\Addons? Because it should be the first.
If you did put them in WoW\Interface\Addons as suggested, then the only proper explanation is that the addons you downloaded are broken. This could be due to the folder or in-game name being changed by someone repackaging them, and you should try a different source (like wowinterface, wowace, curseforge, etc.).