Because someone is trying, desperately, to prove something about the origins of the Etruscans, and at the same time, to overstimate the Slavic influence in the Greeks. And it's funny, because they are producing in this way contradictory results. The Greeks, if you consider the average, are always more eastern/southern-eastern than Tuscans (the sample usually used for Tuscans are southern Tuscans, who are to the west of Greek Thessalians). As you have noticed, they've tried to involve the Tuscans at all costs in that discussion. But Gravetto-Danubian is a good and capable poster. On others I'm not so sure.
There were Mycenaeans in Italy, especially in southern Italy, but also in central Italy (nortern Lazio and southern Tuscany) and in some ports of the Adriatic coast like Spina or Adria. Mycenaean pottery have been found not only in Italy, Sicily and Sardinia, but even in France and Spain (and according to an old book, also in Great Britain and Germany. I don't know if it's accurate). Although it was more often the result of trade rather than settlements.
The Mycenaeans have, without shadow of doubt, played an important role, especially in Italy. Some Italians could even descend from the Mycenaeans, but Mycenaeans were never in such a large number that it could have completely changed the entire genome of the local population.
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