It is true that selling when profit and buying when the price is down is an old strategy that is commonly used by many people. But the problem is that it's not that easy when implementing this strategy, if the practice is easy to do everyone will easily get rich from investing in crypto.
In fact, the old strategy must be supported by other factors, such as good research and analysis skills to determine which coins are good to buy.
It is easy, it just doesn't make you rich very quickly. If you keep on investing when it is at the bottom and sell at the ATH, how frequently does that happen? Sure we have seen it probably more than some stocks, but the stock market in general is the same too. Making maybe 100% a year doesn't really call out for people, that is a great deal, in a few years you would be rich, but that takes a few years and people do not wait for it.
Anyone who has done that for the past 5 years since the last ATH, and did not budge, did not made mistakes, only bought low and sold high would have been rich by now, but people do not like to wait that many years in crypto, they still do not trust it enough.
In the end the key to success is patience and most people don't have that. That's why so many people suffer losses when investing in crypto,
even though these people have bought at low prices and have also bought potential coins, but the reality is that more people suffer losses.
It's as you explained they want to make profit instantly, very few people can be patient holding in the long term. No wonder many people
are easily manipulated by influencers to buy certain coins that promise big profits in a short time, this is why many people are risking their
money to invest in new coins which can pump very high in a short time. But what influencers don't explain is the risk of investing in new coins,
which if we sell it too late and the price has already fallen, our money will be stuck for a long time. So we really have to have the good knowledge
about the crypto world, so that we know how to invest properly.