Because the people who lent money to Evergrande did so on condition that the deal was subject to the US’, and specifically New York’s, courts. Presumably because they trusted New York courts more than China’s courts in the event of a conflict.
I put fair in quotes because even though it is obviously subjective, clearly many entities around the world, including China, or investors of Evergrande, however commingled they may be, or whoever else around the world, find it “fair” enough to seek these services in this jurisdiction.
https://www.lexology.com/library/detail.aspx?g=e36cde01-e97b...