It's not so simple, actually. I disagree on some level with the exclusions too, but here are a couple of things to consider:
Nuclear energy is not considered sustainable universally. In Germany, for example, for whatever reason, the general opinion seems to be that nuclear energy needs to go because there is no proper way to deal with the waste.
I am not sure if there are specifically publicly traded wineries in Italy, but generally companies dealing with such vice products (and most other things, actually) behave themselves in Europe (and to a certain extent in the US) and then play all their dirty tricks in other places where the enforcement of law may not be as easy and politicians are more corrupt. So in a fund that covers the entire world, it's not all that insensible to exclude these.
Considering they've to pore through thousands of stocks, such exclusions are easier and cheaper to do than to examine each company and investigate to make sure that they're not doing something shady in, say, some poor corner of the world.