Probably many different reasons just like for other nationalities.
Chinese and Russians who have funds they can move outside of their country are buying property in many countries for the simple reason of not keeping all eggs in one basket, esp not in their home country where one day all they have could be taken away. Even if property value here goes down it is still better than loosing everything.
And as someone who has lived in China for well over a decade, easy to understand they move to thailand if they can arrange their life here in a way that it works for them