Because there's nothing sensationalist in there. Someone unknown told a politician that there might be another explanation for something that's casting a disgraced leader in a bad light, and the politician repeated it to someone who might be interested. The person he told it to said "Yeah, that could be worth investigating". Presumably they will.
If they investigate and find something, that will make news. But as of now, it's entirely possible that "Olga" is the same type of conspiracy theorist that claims the US government is using mind control technology. It's also possible that she isn't, and that she's right, but that's what the investigation will determine.
It's news at all only because it was a leaked phone call. The previous leaked call wasn't major news because it leaked, but because of what the leaked content was.