You are right that you lose nothing unless you sell bitcoin at a loss. But many people invest the money they might need at any time. That is, money that cannot be risked. Cryptocurrencies are attractive because it creates the illusion that you can get rich quick just by buying coins. But when the market starts to fall, most sell at a loss.
That's called a wrong investment strategy, there are no cases of loss when people know the best way to invest, buying and holding bitcoins until they reach the desired target is the best way to achieve profits, if after the buying process the market has decreased, then it's just a matter of waiting for the next price increase.
That's why many people say bitcoin is the best asset for the long term and losses depend on how one understands the market, unless people invest in other coins and it's hard to see the same moment as often happens in bitcoin. Basically investing in bitcoin is very easy, but many people misunderstand market conditions and are not used to falling prices, so in these conditions they try to make the wrong decisions.
Yes, bitcoin is probably the best investment option among cryptocurrencies. But as you said, you need to learn to understand market conditions first, which can take years. During that time, you usually make a lot of mistakes, which can be called experience. And only after that comes the understanding of your actions. For example, market manipulation encourages you to buy bitcoin when it is expensive. But for some reason few people talk about cryptocurrency at all now, because no one wants to make everyone rich.