Because of the wormhole topology associated with black holes.

I thought that Einstein-Rosen bridges had no evidence to support their existence. You would expect to see "white holes" at the end of the bridge. No white holes are seen => no Einstein-Rosen bridges.

Wormholes are speculative as even Kip Thorne admits. Admittedly if they are going to exist they exist at the singularity.

I'll sit corrected if there has been any new developements.

Dave "lots of wormholes in my garden though" Barlow