When particles in an accelerator collide, the excess kinetic energy is transformed into matter. New particles flash into existence and shower the detectors, generating data. Why not the reverse?

When matter hits the event horizon of a black hole, it winks out of existence. Whether you think it is crushed into an infinitely dense point or just ceases to exist doesn't matter. A portion of the matter-energy is converted into gravitational waves that radiate out in all directions, contributing to the kinetic energy of every other particle in the universe - recycled essentially. Another portion of the mass-energy of the infalling matter is converted into curved space-time - the black hole gets bigger. There is effectively no matter inside a black hole, it exists simply as a curved knot in spacetime. So, this is curved spacetime in the absence of matter. Why can't this also occur on a larger scale? Maybe dark matter is simply curved spacetime in the absence of matter.