I understand that the most precise usage of the term independent variable applies it to situations in which the variable is manipulated by the researcher, although the term is used more loosely in other contexts as well.
On the other hand, if a variable is exogenous that means it is outside the system we are modelling. It might cause some other variable in our model, but it is not caused by any variables within our model.
I get that "exogenous variable" implies the modelling of some causal system, but isn't that also true of "independent variable" as well, if we limit it to the experimental scenario I mentioned in the first paragraph?