I think the most common one is the price swings. People do not like the fact that bitcoin can swing so much downwards and many people have left bitcoin and crypto in general in 2018. They decided the low swings and risks of investing into bitcoin doesn't worth it.

However they were the same people who bought bitcoin because they were going higher in price and they wanted to get bitcoins so they could be rich instantly and leave work. They wanted to be wealthy and never have to work and be free.

Well when you want that type of life you can't invest into gold or stocks, they won't give you that wealth overnight, if you want to become wealthy in the span of couple months you have to invest into something that swings like crazy but those people assumed crypto was just going up without ever going down I suppose.