Most people don't have a coherent ideology.

I think there's a lot of anti-tankie radlibs who are just vaushites and will never be anything but vaushites. But a bunch of them are likely newbie leftists who are still being radicalized. They're noticing that capitalism is completely out of control, but they've been propagandized so hard their entire lives that they still have major "China bad"/"Russia bad"/"NATO good" brainworms and those take time to get rid of. This is likely a tipping point for a few of them, where they realize that the anti-tankie crowd doesn't actually share their ideals and doesn't actually want the world to become more equal, which can lead them to question their current world view further and slowly hammer away at those brainworms.