Rusty is right in the above post. We can do whatever we want with the game files privately, as long as we don't distribute them, Bethesda is pretty chill about it because there's no law that prevents the user from grabbing assets from games they legally own and using them in different games as long as the user has the know-how to do so.
But as soon as someone starts distributing those assets without permission, then it becomes a copyright infringement, for the company that owns those files. Voice and music files are used by gaming companies under licenses (unless they are royalty free), so if Bethesda (in this case) goes ahead and gives permission for modders to use these files, then they themselves are breaking the legally bound license, which means they will get into legal trouble and can be put into court or have to pay a hefty amount out of court and then forced to revoke the permission they gave.
Fun fact, Bethesda asked the Nexus not to host TTW when TTW was first born, because Bethesda was worried we would distribute assets from the games. This was one of the reasons why we made our installer the way it is, it is also the reason why TTW is not on the Nexus to this day.
About FO4 CW team and their decision to not have an installer like TTW... I can only speculate, but I can come up with a few reasons why that might be:
First, getting someone that knows how to create and maintain the installer is a pain. TTW has had some versions delayed in the past because of this same reason.
Second, if the mod requires an installer then it can't be automatically installed by mod managers. So no one-click download and install, no including it in Nexus collections, users that are too used to this easy stuff will get problems installing it, it increases the customer support that a team needs to offer to users.
Third, maybe Bethesda telling them that they couldn't legally allow it scared the team and they decided to not bother with an installer, because what if Bethesda shuts them down later for other reasons and all of that?
