I’m entertained, I need a book in this universe.

That’s a brilliant way to answer.

Maybe they don’t get along, or they use magic in entirely different and incompatible ways.

Even with those limitations, duplication would still allow food producers to make less food go a longer way. Smaller farms could feed more people, reducing pollution. You could duplicate the food at the point of sale, which would drastically reduce transportation costs as well as traffic. Hell, cities could have small farms and fed themselves. It would also drastically reduce water consumption that is used in farming, reducing droughts. Producing and transporting food is a massive contributor to global warming. Farms and ranches take up tons of space, all that land could be returned to its natural state (I bet wizards could speed that up).

If wizards showed up with the cure to cancer and fed the hungry they’d easily have 1/5 of the world’s population on their side. Unfortunately the wizarding society is extremely exploitative of animals, even worse than the average muggle.

I get that wizards were persecuted and don’t want to have muggles expect them to solve all their problems, but they could literally save the planet.

Competition is good, especially with regards to privacy and cyber security. Customers benefit when companies don’t have a captured market. A lack of competition only leads to monopolies and stagnation.

If no one offers a secure product, then customers have no choice but to either not use anything or put up with it. Competition means that at any time a newcomer can offer a better product (that is hopefully open source).

Edit to add: Ideally you could message people on different apps with the same account. But I’ll take fragmentation over a monopoly.