Why can a 14-hour cold brew taste better than a 22-hour cold brew made with the same beans and grind?

Answer: Longer steeping pulls out extra compounds that make the flavor less clean.

Longer steeping pulls out extra compounds that make the flavor less clean. ✓ — Right. More extraction is not automatically better extraction. A 22-hour steep can raise dissolved solids, yield, phenolics, and titratable acidity compared with a 14-hour steep, but past a point those extra compounds can make the flavor taste less clean. The 14-hour cup can taste better because it avoids the dull or muddy notes that come with over-extraction.

The longer steep makes the drink more acidic, and higher acidity always tastes sweeter. — Not quite. Acidity can be a pleasant part of coffee, so the mistake is treating more acid as automatically sweeter. A 22-hour steep can raise titratable acidity, yet the better sensory result came from the 14-hour steep. A good cup balances aroma, body, acidity, and bitterness rather than maximizing one number.

Water stops dissolving flavor compounds after fourteen hours, leaving the longer batch weak. — Not quite. Water does keep dissolving compounds during long cold contact, so the 22-hour batch is not simply weak or dead. The problem is that the extra dissolved material is not all delicious: longer steeping can raise strength and acid load while making the flavor less clean or less preferred. That is why more time can sometimes taste worse, not because water quits.