More restaurants, more music, more entertainment, more culture, "scenes", more romantic partners, more job opportunities, high energy, hustle, fashion, always something to do, etc.
They are, but man the appeal does wear off, at least it did for me.
I moved here when I was 24, and I loved it for the first 8 years. Almost overnight, when I was 32, I realized that I actually don't enjoy living in the city anymore. It's loud, expensive, I don't really do "indie" restaurants, I don't like most art, and I'm married so I don't really need more romantic partners.
I still live in NYC, purely because my current job won't let me move, but I have been looking for an escape.
Cities are great when you're young.