First and most importantly, because it's too good not to have been true.
Secondly, because any of the Middle English literature I've read seems positively a-glow with child-like wonder, relish of simple things and naive piety.
Thirdly, because I am currently reading an anthology of Catholic poetry, edited by Shane Leslie, whose introduction quotes this refrain from a Middle English drinking song:
Bring us in good ale, and bring us in good ale;
For our Blessed Lady's sake, bring us in good ale.
How could anyone read those lines and not believe in Merrie England?