All of this kind of stuff - shady Russian connections, nepotism, the party's full understanding of what they were installing in Downing Street - regularly passes through the news, almost without comment, and is immediately memory-holed. This story was itself originally on page 5, and like most of the recent "revelations" over parties was already known, had already been written about (some book or other, can't remember which). Maybe there was something especially spicy here, maybe it was the timing, maybe someone decided the tap was being opened just a little too wide. In any case the self-censoring instincts of The Times went awry somehow, requiring explicit threats/bribes, and I suspect that is itself fairly routine. What's remarkable here is the brazenness - that it had already been published - but more importantly that the journos have decided to make a thing of it, rather than maintaining their usual "Nobody tells us what to write and to suggest otherwise is Trumpian!" routine.
As with a lot of other things, Boris is making a lot of routine corruption, complicity and incompetence just a little too obvious. He's making them all look bad and that's why he's got to go.