unlike any other Buddhist country, apparently. It all seems to boil down to one person in one particular circumstance leading to huge consequences, as is sometimes the case:
“Shinran’s most influential innovation was his open, unabashed abandoning of celibacy…Shinran… paved the way for hereditary succession to the leadership of the sect… This stable leadership succession was of particular importance during the turbulent times in which the sect originated and consolidated its following”
Buddhism A History by Noble Ross Reat pg 203- 204
It doesn’t explain what, if any, religious justification he had for this, but it does say that he thought most of the trappings of the priesthood and religious practice were pointless so I suppose that could be it.