I'm kinda new here, and maybe I'm not fully grasping what you mean. . . . .
But there are considerable advantages to having a reference be eligible for collection the instant it is last referenceable, and cause for concern when this hold can persist in an invisible form.
I have worked in code where a reference to a structure of size ends up at the top of a call stack. Having it persist would basically be a leak (especially if some derived duplicate were made). Having this effect occur on some granularity would make the effect nondeterministic (e.g. testing the same code fragment in a vacuum would not repeat the leak).