Yes, they're in space
Didn't you put in new filters before we took off?
Yes, but this ship's been sitting open to a dirty environment for a long time.
With the launch vibration and microgravity, all our dust and grime went airborne. From there, it gets sucked into the ventilation and clogs up our filters.
So what you're saying is that as long as we go into space regularly, I don't have to worry about housekeeping.