[verzali]

At 480km there will be increased drag, even as we get closer to the solar minimum. The trade-off may be between using propellant for collision avoidance vs using it to counter altitude loss and for station keeping.

Maybe it is also linked to the falling altitude of the ISS? 480km is about the upper bound of its altitude but they seem unlikely to actually raise it that high before it is deorbited.

[DoctorOetker]

is it conceivable that collision avoidance maneuvers become cheaper in fuel consumption by using the slightly less thin atmosphere to steer a satellite (only use propellant for attitude control, less direct linear acceleration?

i.e. if the propellant consumption for collision avoidant steering at 550 km in practice turns out to be higher than the consumption to negate the drag incurred for using atmosphere for steering, it could be a logical choice.

[verzali]

Yes, you can do that. But you do need to alter your attitude for long periods and that usually means you point away from the optimal position for the solar panels and for the antennas pointing towards the ground. So yes, but only at the cost of some loss of efficiency.