[spiralx]

Because gravity distorts _space-time_ - not just 3-D space - then the event horizon is the boundary at which gravity means that all future paths (technically everything within your future light cone) lie either on or within the event horizon, leading to a stable orbit at the horizon or spiral into the centre of the black hole respectively.

Space isn't distorted at the event horizon and you wouldn't notice any effects from crossing it - other than no longer being able to see the outside universe.

[naasking]

> Because gravity distorts _space-time_

Technically, in GR gravity is the distortion of spacetime, it does not have independent existence that acts on spacetime. It's mass that distorts spacetime.