When Bitcoin reached $19k + in 2017 many cryptocurrencies were pumped to their all time high. People were thinking that if they trade in crypto world they will be rich within months. However, the sudden crash of market in 2018, and the news of bubble busting destroyed their hopes. Many people have lost their initial capital in that crash.
In that crash only few well-known coins survived, but most of the coins that had no good use cases were totally bankrupted. The reputed coins like ETH, LTC, XRP, and some others, have survived in that crash. In 2021 most of the surviving coins reached their all time high including the king of the coins Bitcoin.
Bitcoin survived because it's the backbone of the whole crypto world, and it was the crash of Bitcoin that made other non useful coins to flee away from the market. Bitcoin in such scenario is always the best choice for investors, in 2021 when Bitcoin reached its all time high, with it many others coins were pumped more than 10x to 100x in that bull run.
This time some coins that were vulnerable caused the market to crash badly, one of those coins was Terra Luna, it caused a lot of stress in the market and many people have lost Billions because of its unwelcomed crash. Many exchanges were bankrupted because of Luna, and after that crash of FTX made the situations even worse. Bitcoin fell to $15k-16k levels with that bear run, and many users gave up on crypto, but now the market is recovering, and if things go well then the Bitcoin will reach all time high this time.