There is no doubt in what you said kos normally holding beats trading, but not everyone has the spirit of patience, there are some people that can't withstand pressure for that long, especially any time the market is fluctuating, which makes their heart to beat very fast. And also, not everyone its ready to undergo or its able to meet the requirements for them to be able to hold. So for you, you might think holding its for everyone but to some, its easier to say than done.
Holding is especially difficult when the market enters a prolonged correction during bear markets. Many are willing to sell at a loss, just to escape the stress and accept the losses. But if someone sells, it's another opportunity for stronger investors to buy back at a lower price and make even greater profits in a bear market, that's how it works, some sell, some buy. The stronger players will make money, the weaker ones will lose, that's how the market works.