Second, because Varoufakis is an economist, not a politician. His entire career, and his academic qualifications are built on the conviction that a) austerity does not work; b) the Eurozone will collapse unless it becomes a union for recycling tax from rich countries to poor countries; c) Greece is insolvent and its debts need to be cancelled.
By those measures, any deal Greece can do this week will falls short of what he thinks will work.
On top of that, politicians are built for compromise. Tsipras has to work the party machine, the government machine, the machine of parliament. Varoufakis' machine is his own brain.
If he wound up the creditors it was for a reason: they'd convinced themselves that Tsipras was a Greek Tony Blair and would simply betray his promises and compromise on taking office.
The lenders detested Varoufakis because he looked and sounded like one of them. He spoke the language of the IMF and ECB, and turned their own logic against them. But he achieved his objective: he convinced the lenders Greece was serious.
Varoufakis critics in Greek politics accused him of flamboyant gestures and adopting a stance he could not deliver on. His critics in Syriza believed from the outset he was "a neo-liberal".
Among the lenders it was always the north European politicians who could not live with Varoufakis. Though he was at odds with the IMF's Christine Lagarde and at odds with the IMF over all matters of substance they at least spoke the same language.
His policy was total honesty, and when it could not be honesty in public it was honesty in private. He exploded the world of Brussels journalism, which had become back-channel stenography, by publishing the key documents, usually sometime after midnight.
In the process he has templated a style of politics that may be equally adaptable for the right as on the left, for those with the will to try it: operating from principles, being as open as possible with information, engaging the public in language they can understand, and putting his entire persona on the line.
Vist Paul Mason's Channel 4 blog for more from Greece. Mason has written the foreword to the new edition of Yanis Varoufakis' The Global Minotaur from Zed Books.