They've been doing a fair amount of Mahler with Chung. It's just that he's recording them in Seoul, which I'm sure is a less expensive proposition than recording Mahler in Germany. That orchestra is very good, but they're no Staatskapelle in my book.
I think there's a number of very talented, relatively young Mahler conductors today: Markus Stenz, Jonathan Nott, Ivan Fischer, Danielle Gatti (just got the Concertgebouw), Chailly, Nezet-Seguin (Philadelphia), Dudamel (yes, I like his Mahler), Mark Elder, Kent Nagano.