The view that being a committed theist must necessarily cloud one's judgment, or at the very least undermine one's claim to rational objectivity, has been influential and powerful since the Enlightenment. To a remarkable extent, Christian thinkers went along with it, in the hope of attaining a Cartesian-like virtuous epistemic freedom from all presuppositions. That era is passing, since in both analytic and phenomenological philosophical traditions, a change in epistemological fashion has led to greater acceptance of religious experience and greater awareness that atheist and secular humanist points of departure involve just as much substantive theoretical commitment as theistic ones.--James G. Murphy.
Christian thinkers didn't just "go along with," they helped promote the idea that commitment to theism and rational objectivity were seperable, in part, in order to secure the Christian mysteries from rational criticism and maybe, in part, to ensure that commitment to theism did not depend on highfullitin reason so that it would remain out of reach for ordinary people.
This is not to deny that "we have come a long way from the mid-20th century, when much Anglophone philosophy doubted that talk about God, let alone talk about religious experience, could even be meaningful." However, this is not wholly due to "change in epistemological fashion." The idea that there are 'epistemological fashions' implies, I think, that such changes just happen due to changes in taste and group social dynamics. Undoubtedly some of that plays a role. But the changes were, in part also due to a growing realization that trying to argue against positions in virtue of their purported lack of meaning was simply an instance of bad faith, not to mention a strategy often bordering on the self-contradictory. Substantive disagreements should be argued substantially.
But this does not exhaust the origins of the epistemological changes. I can think of a few at least two more sources: