He wore the same shirt because when he first was given it it was a hand me down from his cousin who is like 4 times his size it took him that long to grow into it. And it didn't wear out because of magic. He used a repair spell when his clothes got holes.
All his clothes EXCEPT his school robes, Christmas sweaters from Ron's mom and his dress robes are hand me downs. It's in the books.
The real life Daniel Radcliff has done this too. He will wear the same clothes multiple days, I believe he’s done it for whole months. That way, when paparazzi take pictures of you, the exact date can’t be discerned from the photo. It makes the pictures essentially useless because magazines won’t buy them. Most people don’t want to see a star looking exactly the same in every magazine and every photo, it makes the magazine look like it’s using stock photos, and the magazine can’t even be sure if the photographer really took a photo when and where they said and aren’t just selling them photos from the same days shoot and saying it was from another day. It was quite smart of him and really upset a lot of paparazzi at the time. But yeah- in context to the film it’s cannon as @mrscollector states.
All his clothes EXCEPT his school robes, Christmas sweaters from Ron's mom and his dress robes are hand me downs. It's in the books.