| I notice many of these worlds (when eventually conquered conventionally) are FULL of embassies and the like. The AI seems to realise that they're at risk. |
True, and sometimes it builds influence starbases to counter the effect, but the pirate symbol means that even with such efforts it is still in danger.
Personally, I find it takes a long time for colonies to flip. Even if you build that galactic achievement that is supposed to caught colonies to flip immediately.