They're not helping torture anyone right now due to a lack of demand, so it doesn't matter what their policy is. If they're needed again, they can quietly repeal or carve massive semantic exceptions to this e.g. is it an interrogation or an interview?
Sure, they could. Things can always change for the worse in the future, but at least now the default state is different. Knowledge that something may change in the future doesn't render everything in the present futile, even for symbolic stances of self-governance. This is certainly toothless symbolism, but it doesn't make it meaningless. It's a reaction to the disgust most of the membership felt towards the organization. There will always be individual psychologists that will do what they're paid to do anyway, but I'd still prefer the body with the biggest political influence stake out a "not horrible" position on any given subject.
The APA is a meaningless organization. They have zero authority over licensing. They also aren't the only professional psychological organization. APA membership carries with it no particular value; clients don't care about APA membership, they care about licensing.
The value of an APA membership is primarily that it makes access to published research affordable. If someone wasn't interested in accessing journal content, or required to present at conferences requiring APA membership to further their careers, I can't imagine why they'd pay to join.
I briefly looked before making my comment in another thread, I don't think the APA has any say over licensing (it's done by the states).
As to reasons why they might anyway, they believe the interrogation is worthwhile, a sense of duty to country, money, etc (I'm not saying those are reasons I agree with, I'm saying they are reasons someone might use to justify participation to themselves).