(Edited response) It wasn't immediate - except for those religious and ordained who found a freedom in society they never knew before - but started as a trickle.  Most were please - and many came back - because of the promise of renewal and inclusion of the laity.  Once that promise was blocked and then reneged on,  the losses were more and faster.  It is slower, but steady, now, not just in leavings but in not attracting and holding younger generations of what started out as Catholics.  I assume you know all of this anyway, so I will leave my response here