The Abyss has existed alongside the Courts for so long that the very competitive Chaosi are blase and merely wary of its dangers.
Yet allowing any Amberite to master it within the scope of a few years (canon suggests that only Benedict might have really had more time to study Chaos) is a very forced story line IMO.
This might be why many GMs stay away from it. Chaos campaigns could have other potentials.
I think the 'Brand / Dierdre return from the Abyss' is a hard road to do well and undercuts a central theme Zelazny layers into the series: legends die hard but they do die. There are a few good stories I've seen over time with this theme that don't undercut the Zelazny drama.
In effect, the 'Brand / Dierdre return' storyline (including the one offered in the rulebook) breaks at least three rules for canon genre by trivializing Zelazny's arc:
3. no one is safe from an united amber family (not a hundred Chaos Lords, not Brand, not nobody)
2. killing amberites is big mojo (it only happens every 2,000 years or so)
1. sacrifice (like Corwin or Oberon attempting to fix the Pattern) is the biggest mojo of all