NewMe, it does indeed seem like more of a betrayal. Perhaps that is because it is so obvious, with an enabler, that a choice is being made, and that the choice never seems to involve being fair to you, or even being minimally decent to you. The choice is always to favor the N.
That's a pretty fundamental betrayal, especially coming from your parents, whether it involves favoring an N parent, or an N favored sibling, or any N who happens to be in the vicinity. I have seen quite a bit of what I call 'drive-by' enabling, where people defend an absent abuser - quite often a person they have never even met - rather than supporting the person who is there, whom they know, who is talking to them about the abuse. Ns, incidentally, at least in my experience, seem to be extremely 'into' doing this. Abusers in general seem to be 'into' it... it's a form of invalidation.
The enablers may not be able to help themselves, any more than the N can, but in the immortal words of Sovereign and Safe, "So What?" You see them making the choice, every single time it occurs. You see that they could choose differently. Eventually, you come to the conclusion that they don't want to. At that point, does it really matter why? Any more than it matters why the N does what they do?