If Google was satisfied with the revenue from "search" alone, it wouldn't have grown this big to have a $1.9T market cap. Countries or businesses will always try to diversify their income sources and revenue streams. In spite of being cash rich, the chinese weren't able to develop an engine and still rely on the Russians. While they might already have a know-how of most of TB2's tech, they'll leave no stone unturned to get a better understanding of what TAI got right and how does TB2 have better operational successThats because China is not really concerned about exports, they have more than enough money for their own defense industry, Turkey however needs these exports to finance future developments
and the chinese exporting weapons platforms isn't necessarily about the money but soft power projection and bilateral ties