Because Darwinian Evolution is gone! It's gone long time ago. What Evolutionary Theory teaches today is more like Evolution 3.0 or 4.0. It has gone through many major revisions and some things were unknown to Darwin, which makes Darwinism invalid. So they agree with the current science then? Awesome!
I would argue that Evolutionary theory remains the same evolutionary theory since Darwin. This is not because I believe your statement about major revisions to be false; quite the contrary. Evolutionary theory today is drastically different since Darwin (who didn't understand inheritance or know of genes). The reason evolutionary theory today is the same theory it was after Darwin (despite the massive changes to what that theory involves) is because that's what theories are: networks of confirmations, results, hypotheses, tests, reviews, critiques, replications, etc. They are frameworks. Evolutionary theory differs (as you say) radically from what Darwin proposed, yet remains evolutionary theory because the countless discoveries and tests that have refined our understanding of evolution have all been undertaken within the theoretical framework of evolution. Alas, education (even at the university level) tends to depict a model of The Scientific Method in which some hypothesis is developed independent of theory, tested independent of theory, and confirmed (or not) independent of theory. This is not how the sciences work. Rather, experiments typically refine, alter, adjust, extend, broaden, etc., some theory. We've been doing this with evolutionary theory for over a century and all the countless experiments in numerous disciplines have continually demonstrated not just that evolution is true, but the nuances, details, mechanisms, processes, interactions with mechanisms and processes, and so forth that evolution is.
So while it is true that evolutionary theory is not the theory of evolution of Darwin in the colloquial sense of theory, evolutionary theory is and has been evolutionary theory since Darwin. That's what makes it so thoroughly confirmed: despite the extension of the model to fields as diverse as evolutionary psychology to astrobiology, we have continually demonstrated
more about the ways in which evolution occurs.
One theory, countless ways in which the theory as a framework inform countless research areas.