Clearly they are aware of the market for DVD copying software, i'm sure they know that most of their users will be using it to rip copyrighted DVDs to create "backups". However, it is against their EULA and of course against the law to use Nero to copy the latest Batman DVD.
On the other side, Nero is good for burning just about everything else. Some universities require theses and so on to be given in on DVDs. Some engineering courses require you to submit massive CAD files that would be impossible to email so you have to send in a DVD. A lot of camcorders still use DVDs to store data (though they're quickly being phased out by SSDs). Consequently film makers and photographers, both amateur, semi pro and pro need DVDs to back up their photos, send out preview copies of films, etc. Wedding togs often send out a taster DVD so people can pick the photos they want from the day (it's cheaper than printing a proof book).
This is the case with practically anything you can buy. If i bought a chainsaw and used it to cut down some trees, no problem. If i went on a supermarket rampage with it, i'd be jailed for life. Ultimately it's you exercising your free will.
If the law banned everything that could be used for an illegal purpose, we wouldn't be allowed out of our houses.