Cats Suddenly Picky About Food

Have 2 cats, male & female. All of a sudden, like a screeching halt, after
months of eating any hard food of any price level I gave them, they suddenly
refuse to eat anything at all except soft food. A few days ago we couldn't
find the stash of hard food we had on hand, and picked up a small can of
soft, and went back to the hard afterwards. They immediately started
rejecting the hard they had previously been fine with.

Thinking maybe the hard food we had left was old--it was 2 months old--we
bought a fresh box and they started eating it fine, and we gave them no soft
food. But, after about 3 days, all of a sudden they're rejecting in--and
protesting loudly.

Sorry to not be a "cat lover," but I have no intention of indulging their
pickiness. If need be, I have a cat carrier and can confine them to that out
of the house so it's not noisy--they protest quite frequently and
loudly--until they get the point. I'm not worried about them starving to
death, I figure sooner or later they'll have to eat or else.

Even so, though, what in the world would make them snap like that so
suddenly? I know we did give them soft food for a day or two, but for them
to readjust to hard food and then suddenly 3 or 4 days later snap back to
being picky, just doesn't make sense.