I feel like after having lost everything twice and being powerless to stop it both times, I feel like Law swore he’d never let it happen again. Which is why I believe he probably left his crew on Zou; he didn’t want them getting mixed up in the mess, or running the possibility that Dolflamingo would use them as a way of getting to Law. It was a catastrophe he could prevent.
And as much as I want Nami to bring the Hear Pirates back to Dressrosa, I feel like Law would probably get upset if they did show up for the simple fact that he did that to keep them safe and then they’re there. Dolflamingo already showed that he’d have no issues trying to kill the Straw Hats in front of him. I have no doubt he’d try to use Law’s crew as leverage against him. It’d just cause a mess he went out of his way to avoid.
Though I feel like a part of him would be happy that they cared about him enough to throw themselves into the mess to help him.