OK, so we know you can't conjure up food out of thin air. But Wizards do conjure up other things at various times. Even more commonly they seem able to quite easily repair damage or otherwise change objects to suit their liking. They're certainly able to create temporary illusions of things as desired.
So: why does Ron have to put up with his horrible dress robes for the Yule Ball? Why can't he conjure up some new ones, transform or repair the ones he has into something new, or cover them in a less embarrassing illusion?
This leads on to a wider question: again, we know you can't conjure certain things. But you'd have thought it possible for wizards to adjust the majority of their positions to their taste. At the end of Fantastic Beasts, for instance, a few Aurors rebuild the entire center of New York! So why is anyone in the Wizarding world "poor" in the muggle sense?
(I'm aware that the real answer is "because it reads better that way". I'm just curious if there's an in universe or canonical answer. And I have looked at the following related questions:
Why are there "dilapidated" buildings in Harry Potter? - I don't accept this answer. Especially now I've seen the end of Fantastic Beasts. That makes it look very easy to do repairing magic on a vast scale.
Why can't wizards magically fix clothing? This convers fixing clothing with Reparo. Not transforming it or covering it with an illusion.
Rich Wizards, Poor Muggles This does not seem relevant to me. It covers why there are rich and poor wizarding families, but not what they do with their money. Nor does it explain why some wizard families choose to "live poor" in muggle terms when they don't have to. )