They are still buying a ton of robots and machines from Japan and Taiwan, instead of buying them locally?
Japan and Taiwan supply the world's industries with some of the most advanced machine tools that money can buy. For Japan, particularly for car manufacturing machinery. Chinese equivalents that apply in the car industry probably are not as competitive as Japanese ones yet. They probably are not even that much more affordable anyway.
The engineers in these manufacturers are already used to and know the established machine tools. It would be like asking someone to switch from Excel to another platform that is nearly as capable (but not) and also unfamiliar and not much more in terms of cost savings.
China's machine tools have made much progress but we should remember that Chinese car manufacturing has gone ballistic in the last twenty years. An increase in purchases is expected since production of cars have gone up so much. I doubt they are not buying machinery locally. I would expect the vast majority of machinery to be Chinese by now and the rate of this increasing over time. To make the statement you made, we need to look at the trends of sourcing from Japan AND the trends of sourcing from China. You would see sourcing from China steadily climbing while sourcing from Japan remaining relatively stable but a slight decline over time. This doesn't take anything away from the fact that Japanese machine tools are exceptional and well respected by engineers in those fields. They are the creme de la creme along with German and Swiss machine tools.