I´m not joking if i say that the thing that discredited phylosophy and the philosophers was the Relativity, the Quantum Mechanics and their realization: the atomic bomb. That is the event that raised physicalism , a branch of Logical Positivism and Analytical Philosophy, and discredited any other way of thinking. Phisicalism manifest itself in the idealization of phisical sciences as the model of everithing and the idea that the only valid methods of enquiry were the ones of Physics. In phiosophy that implied the triumph of Positivism, an old philosophy, since Compte, that postulated the primacy of the hard sciences.
That triumph was so strong that the positivist metaphisics became THE reality. Like the fish presupposes the water. People, not even scientist know that they are ferocious logical positivists. Since then, biologism and computationalism or economicism, other branches of positivism have been of fashion since the cloning of Dolly and the popularization of computers or the power of the global markets.
Before the triumph of positivism as the only phylosophy (with his inevitable consequence, the relativism), The philosophical debate was on the top, in the same way that religion was before. People killed one another in the name of philosophical concepts. All the ideologies of the XIX and the first half of the XX century invoked prominent philosophers.
That is not only fashion. IMHO, this is religion. As Voegelin said, what is in common in all these movements, branches and ideologies, from physicalism to biologism to computationalism to comunism to nazism to ecologism etc is the notion of utopia, that is the common ground of modernity. All of them propose a end of history and a perfect state of things, or at least a straight path to eternal improvement trough knowledge and investment in the particular things that they are promoting, while despise any other kind of effort. The paradise is just tomorrow (if you follow me). You only have to take a look at Scientific American or any other publication of this kind. Behind these ideas they are the immortal desires and hopes of religion, and , specifically, they are forms of inmanent, sectarian, gnosticism.
What drives this change? the same drive than in the ancient times: If A people defeat B people, then B people agree that A gods are stronger that B gods. The atomic bomb, the cloning, the magic of the computers are manifestations of the gods of modernity in the minds of the stone-age human brains, and the prominent political and scientific figures become the priest of his religion. Had the Moors defeated the French in Poitiers, we' ll all believe in Allah.