Why are the Corded Ware and Kurgan theories incompatible?

Question

Why can't the Corded Ware Culture be a part of the Kurgan hypothesis of the PIE Urheimat? These two things overlap in time and place. Gambutas included the Corded Ware culture in her theory. I'm not sure if there is a "Kurgan Culture" or if the Corded Ware Culture built Kurgans.

...the Corded Ware culture was once presumed to be the Urheimat of the Proto-Indo-Europeans... Today this idea has lost currency, as the Kurgan hypothesis is currently the most widely accepted proposal to explain the origins and spread of the Indo-European languages. Corded Ware Culture- Wikipedia.com

Edit: I think that this "Kurgan Hypothesis" may be refering to the spread of later Tumulus Culture, with confusion arising from the interchanging of those words. This Middle Bronze Age expansion is my understanding of how IE languages spread outside the steppe.

Answer 1

The Corded Ware culture appears to have introduced Indo-European languages to a large part of Northern Europe. However, it doesn't appear to have been the origin of the IE languages, because there are no traces of it in Greece, India, or Iran, where IE languages have existed since about the same period when Corded Ware was active.

Therefore, the Corded Ware culture must be one of several successor cultures to the culture where IE languages originated. Other successors spread IE languages to regions that Corded Ware never occupied.

The Kurgan culture is the current most common choice for the origin of the IE languages, and Corded Ware is a plausible successor culture to Kurgan, from what we know about them.

Answer 2

The Indo European Urheimat is represented by the Yamna culture or the "Yamna Horizon". The Corded Ware was an offshoot of the Yamna culture that spread across Northern Europe. A Corded Ware Urheimat would theory have meant that the Indo European Language was from Europe, not the Caucuses or the Pontic Steppe region.

North European hypothesis (Nordicism)