I’m sure you will get a better answer but the simple one or at least how I think about it is in terms of DNR… The tone curve is a tool “primarily” used to manage contrast of the image in the existing DNR where as tone mappers are about impacting DNR of the image and the required math to do that… If you don’t need to manipulate DNR in your image to a great extent then do you really need a tonemapper??
Way over simplified but I think that is generally the case…