Angiofibroma bleeds excessively because -
The characteristic of JNA is that the vessels are just endothelial - lined spaces with no muscle coat.
As the contractile component (muscle coat) of vessels is absent, vessels have no ability to contract, i.e. vasoconstriction does not occur, and this accounts for :-


Severe and recurrent epistaxis
Bleeding cannot be controlled by application of adrenaline, a potent vasoconstrictor.
It lacks a capsule
Vessels lack a contractile component
It has multiple sites of origin
All of the above