There's a multitude of reasons for this: to highlight their brilliance if they win with a weakened side or create mitigating circumstances if they were to actually lose.
However, the pièce de résistance is the media's desire to sound how brilliant their campaign is, where they need to rest players due to their 'terrible' circumstances.
All these games won and all these success stories, but they've had to do it with such a hectic timetable and such a depleted squad, when it's not like that.
They could field a nigh on full strength team tomorrow (only Fabinho from their ideal XI) if they chose, but they are choosing to rest for their own benefit.
Rightly or wrongly, they do not see the FA Cup as a priority and, no matter how difficult it is to say, they probably don't see us as the most difficult opponent.
They are playing incredibly well and their record speaks for itself (you've got to be magnanimous), so I don't see the need for all these media hardship stories.
They'll play a weakened side because they can and not because they have to, and I don't see why they don't acknowledge the support they've had - however small.