Also because the wizards are in hiding. Their world is hidden intentionally because they are outnumbered and were being attacked. This led to a very insular and small community that didn't really have the numbers or the desire for innovation. They can survive just fine on their own and can teleport so there isn't a major need to adapt and change and theirs no scientific method and not enough people who want to change anything. The Wizarding society we see in the books is still largely dominated by this insular pure blooded type of mindset even if not all of them are blood purists. The Weasley's for example are very liberal and open but Mrs. Weasley still greatly dislikes anything muggle and Mr. Weasley is obsessed with them but largely clueless. Reminds me somewhat of early European settlers being fascinated by indigenous populations in the 'noble savage' kind of way. There's just no societal drive to change or improve. The society is stagnant and dominated by conservative old fashioned beliefs that haven't changed since the international statute of secrecy. More on reddit.com

Because there's still scarcity. There's no real mass production, everything is done by hand or on a relatively small scale and food simply can't be magicked out of thin air.

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Magical Russia is recovering from the revolution and deposing of Baba Yaga. It is quite probable that either a new Dark Tsar/Tsarissa will take over soon, or the country will be overrun with out-of-control werewolves again.

Magical Scandinavia is suffering from yet another burst of troll population. Despite the countermeasures, thousands of troll had breached containment, and are now roaming Northern Europe. Some even managed to migrate to Canada, Northern Britain and Greenland. Of course, the Wizarding World is outraged and blames the Scald Council of Scandinavia of not taking enough preventive measures and dropping the ball on the issue. SCS blames it on the Muggles and their tampering with the enviroment.

Magical America is knees deep in solving the Shamans' vs Salemists conflict. The increased immigration of brujas from South America nad Mexico had tipped the balance of power away from the WASPy magical families of the Salem Confederacy. As of today, the tensions already caused several instances of magical violence, some of them with enough collateral to violate the SofS.

Most of Magical Europe is currently at war with The Most Miraculous Caliphate and its djinni terrorists. The agents of the Saif al-D'jinn had successfully assassinated several key members of the European Council of Mystical Arts. The power vacuum allowed borderline blood-pursits to take over. Some say Magical Europe is on the brink of producing the next Grindelwald.

Magical China is isolationist, and besides, the Jade Court formally legalized all Dark Arts, so from their perspective Death Eaters and Voldemort are a legitimate faction. They stay away from foreign politics. It is specualted that the Jade Court is currently conducting mass genocide of yetis, but nothing had been proven.

Magical Australia, Canada and New Zealand had sent some symbolic help against the Death Eaters. Magical Australia is currently the place where most magical R&D happens, and many "bleeding edge" spells and potions come from there.

The Unselie Court of Ireland is actually still at (cold) war with Magical Britain, so no help had come from there against Voldemort. Some suggest that Queen Maab actually secretly supported the Death Eaters, but thats probably heresay.

The Carribean Confederacy of Witchdoctors, and The Miraclemen of Bhārat (India) offered humanitarian help, but no military assistance during the War on Death Eaters. Indian Miraclemen are also at war with The Most Miraculous Caliphate.

As for powerful individuals, we know that the Prester John, Jan "Moonwalker" Twardowsky and Maman Brigite sided with the Aurors, while Kostiei the Deathless, Rasputin and Abel Griswold and his Great Werewolf Brotherhood sided with Death Eaters.

Most surprisingly, both Vampire Monarchs: Vlad Dracula and Elisabeth Bathory rejected Voldemort's offer of an alliance.

And then there is the "Three Poles Problem"

Pole problem nr 1: Pole on the Moon. In 1692, one of the most powerful Apparition Masters, Polish Wizard Jan Twardovsky managed to Apparate to the Moon and claim it in the name of the Polish-Lithuanian Kingdom. According the international wizarding law, this means that all magical resources and energies of the Moon belong to Magical Poland now. This is extremely politically and economically inconvenient to other magical countries, creates much political tension, and had made Magical Poland a disproportionately influential economic juggernaut.

Pole problem nr 2: The North Pole. The Regent Mage of the North Pole (known to Muggles as the Santa Claus) is a known violator of the Statute of Secrecy, as well as a problematic meddler in the magical economy. There is even a talk of Britain-backed elf uprizing brewing against him.

Pole problem nr 3: The South Pole. For centuries, the South Pole was a forbidden zone for wizards, and not without reason. There are...things slumbering deep under the ice. Old things, nameless, nasty things that should not be disturbed. And of course, once in a while some especially idiotic and suicidal Dark Lord Wannabee travels there to poke them with a stick. The fallout usually requires the cooperation of most of the Wizarding WOrld to clean up.

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