The movie opens with Picard having nightmares. It doesn't suggest Picard would have those nightmares often - and he certainly doesn't seem to remember any nightmare featuring the Borg Queen.
The implication IMHO is either
a) that the Borg are sending out transmissions specifically to spook out Picard and prepare him for his task in rebooting history, or
b) that the Borg, now a stronger presence than ever (no full-sized Cubes involved in the preceding events, and no Queen present, at least not physically), are unwittingly sending out these strong transmissions.
Add to this that something has clearly happened in addition to the adventures we saw in the episodes: the Borg have "advanced" and the UFP has "fallen back". We don't know how this happened, and whether it involved Picard personally, but clearly it must have been bad, because the Borg "advancing" rather than just raiding must mean they have taken possession of new territory. And that means they have assimilated people, perhaps planetfuls of them...
I'm pretty sure they didn't know that yet. Only after First Contact and after Voyager reports in do they get that idea.
Picard is Locutus. He isn't allowed to remember about the Queen, but he does seem to remember a lot about being Borg otherwise. He'd be the first to see the quadrillions of Borg as just a single foul stain on the universe, something in need of hard wiping even if (and especially if) it meant killing a quadrillion humanoids.
What stops him from pursuing that in "I, Borg" indeed seems to be the fact that Hugh isn't Borg any more - he has achieved what Picard hopes to achieve with that über-genocide, the termination of horrible mental slavery that is worse than death. There's hope there, and Picard clings on to that hope. In the other episodes, he doesn't have the means. And in the movie, he has abandoned hope, and sees the killing of Drones as his humane duty.
Timo Saloniemi