Why does pouring red wine into a wide decanter change it faster than just pulling the cork?

Answer: More liquid touches air

More liquid touches air ✓ — Correct. A bottle neck exposes only a small patch of wine to air, while a decanter spreads the wine into a shallow pool. That bigger surface lets oxygen and volatile molecules interact faster, so a tight red can smell more open in minutes. It is not instant aging; it is mainly faster contact between wine, air, and aroma compounds.

Cork flavor escapes — Not quite. A bad cork can give wine a musty cork-taint smell, but ordinary breathing is not about flushing cork flavor out. The useful change comes from oxygen contact and from volatile compounds leaving the wine. A clean cork sitting in the bottle neck is not the bottleneck; the tiny liquid surface is.

Alcohol leaves the bottle — Almost, but normal decanting is not a meaningful alcohol-removal trick. Ethanol helps carry aroma molecules into the glass headspace, but the wine's alcohol percentage does not suddenly drop at dinner. If enough alcohol and aroma had evaporated to matter, the wine would likely be tired rather than improved.