The temperature dropped over the past few days to 0°F or so. Great for mending cracks in the ice, but not so great for big pike. During the 2 or 3 days following a severe front like that, bigger pike can be harder to catch. Not impossible, but average size does drop off when comparing notes over time.
When drawing pike in to spreads of tip-ups with rattlebaits, running hole-to-hole with spinning gear, braided line, and thin, hand-tied wire leaders, we see much less activity after a front. Even if a warm front follows quickly on the heels of a cold front, activity levels remain low. Stability is the key.
So we all wish we stayed to catch one more pike when the weather was nice last week. That big minnow on Rick Hammer's rig is far less attractive after cold fronts, too. We often drop to a smaller, dead lake herring in the aftermath of a severe front and place it right on bottom.