Okay, I take your guys' point on the ubiquity of the ships... but not the ability of the movie Reavers to cooperate.
But didn't the series establish that the Reavers weren't
that good at maintaining their ships? That one ship flew by leaking radioactive material, and they referred to its state as 'suicidal'.
Exactly. Look, it is of course a stretch; most sci-fi /is/ by definition.
But the impression overall I got about how the Reavers are depicted is that they're loonies who go aggro on anyone who is /not them/, operating as a vicious, violent pack but the sinister thing about them is how they retain some vile imitation of intelligence and intent: they can rape, then skin, then eat, a victim in a specific order rather than just killing them and moving on. They can steal a spaceship and retain enough mentality to push the basic buttons that make it fly and move the flight stick around - I'm assuming that the computer systems on these /500 years advanced/ spaceships can, in basic modes, make flying one almost as easy as playing a videogame is today. An arcade game too. Not a flight simulator.
So the crazies go mad, grab some ships, and become crazy pirates looking for more people to eat, pushing the flight sticks towards the planet icons on their viewscreens.
But anything past their immediate goal and desire, such as thinking ahead to fix a leaky reactor, is beyond them. So over time their stolen ships break down. We see tons of dead ships around Miranda in the movie. In the series, dialog is also used to the effect that a ship full of reavers MIGHT not be a threat if they've just returned from a kill and are "full". Maybe the Pax-induced violent rage can be sated for a limited time by indulging the bloodlust.
I don't know. I mean, it's not that impossible to me.
However, I will agree that the inherent problem of ominous offscreen monsters such as the reavers is that it's difficult to show them. I didn't think the reavers were too bad, in the movie. But there was definitely no way to ever live up fully to the creepy space monster vibe established in the series.