They didn't stop advancing technologically for gods sake. Hell, they are still hundreds if not thousands of years ahead of us, modern times. They use magic and when they see a nifty muggle innovation they enhance it, make it much better and include it to their society.
Complaining about why they don't bother advancing muggle stuff is like complaining why we didn't continue researching vacuum tubes after we found transistors. It's mostly obsolete.
To be honest, that's just normal human behavior exaggerated by the fact that they literally don't need it.
Like, what are they going to do with a Mars base or colony? Space Elevators? Hell, why should they even colonize the Solor System 1000s of years in the future let alone now?
They already got infinite space, infinite material, entropy defying magic. Plus their population is also small for some reason.
They got literally zero reason to explore space other than curiosity and most don't bother because just the magic they have and the Earth they inhabit is mysterious enough.
1) Most likely because you still need some skill and work in making magical stuff even if you can literally get anything mundane without any cost. And seeing as most humans let alone Wizards are lazy there are definitely demand for it.
2) Currently? They sit, entertain themselves, fight among each other and when needed control the world.
3) There are no such a thing as Wards in canon. There are protective spells and even a Hogwarts student can put them easily.* And if they can protect against it, probably, depending on the payload. But the biggest problem is actually finding it and then somehow hitting it and doing all that before all Wizards just go away with Floo or teleportation or their space defying cars or brooms etc. Also add the fact that their major centers reside in major cities which you wouln't want to bomb.
4)I assume a combination of magic BS and the fact that they can easily get people into all the relevant places that will modify the data. It's very likely Office of Misinformation deals with that kind of stuff.
5)In my opinion? Because Rowling wanted a setting familiar to the reader and didn't want to bother with coming up with the changes. Like how Dresden Files somehow has a modern world setting even when by all accounts modern world as we know it shouldn't exists.
6)They aren't rare. New spells, potions and such are invented every decade. Hell, Time Turners and True Time Turners are only decades old and modern times respectively and they literally blow everything out of water other than maybe Felix Felicis aka Liquid Luck (which is also only invented in 16th century, not anything ancient or legendary)
*Hermione casually put up Protego Totalum, Salvio Hexia, Repello Muggletum, the Muffliato Charm, Cave Inimicum, and the Disillusionment Charm which, in a matter of seconds, rendered an area silent, invisible, repelled muggles, set up an alarm, warded against hexes, and shielded it.
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