This right here is the shit that always never made sense; wizard, despite all their magic power, still rely on candles for light, fireplaces for heat and haven't gotten past the level of radio for entertainment.
(I'm not a Potter sperg, I'm answering from a general worldbuilding perspective)
They don't rely on mundane low-tech things, they rely on magical things. It's like a parallel branch of technological development. And for hundreds of years, it promised a better life than real-life contemporary technology
and delivered. Real-life healthcare still probably hasn't caught up with Harry Potter's magical healthcare. What else is there? Real estate? Live off the grid wherever, hide from the mundane authorities, teleport for transportation. Food? You have slaves. Everything else is sensory and can be handled with illusions.
Also, this kind of tech makes wizards resistant to democratic change. Real 20th century technology requires the organized, sustained, voluntary effort of a very large group of people. Magic has no such requirement, and as a result, the wizard elite are not beholden to the broader wizard society at all. (Their propaganda probably turns this upside down: "Look, any idiot can buy a gun or a nuke. Magic is personal and responsible and only taught to people with the proper mental discipline".)
Wizards are like Hasidic Jews, Jehovah's Witnesses, Scientologists, Hollywood pedos, and British nobles rolled into one. You use the wrong talking fork to eat the mandrake pudding, this offends some senile 92-year-old sandcunt and bam, you're ostracized from society and they cancel your magic license. You have no friends. You have no job skills. Your family has been mindwiped. You can't talk about your life with anyone. Then some noble "prankster" turns your noncaster kid into a toad for wizard likes on wizard youtube. Who you gonna call, the mundane police? "The evil wizard Loganius Paulus turned my daughter into this toad, please disenchant her". Good luck.