but not jet li? he is chinese as well....?

I'm aware of the Chinese entertainment industry and as Jackie Chan is bigger than Jet Li in the entertainment industry. He's a famous actor he he sings occasionally as well. He's also very much involved in charitable events.

Maybe Jet Li was working on a movie or something. Maybe he didn't feel like going.

While both of them are Chinese, Jackie Chan can sing while I believe that Jet Li is not a singer. Similary, we do not see Chow Yuen Fatt there, because Mr Chow cannot sing.