I agree with some of the reasons but not all of them like difficulties in spending you could easily use a bitcoin debit card. These two reason learning curve and poorly understood should be together it looks unnecessary to see them listed as different reasons.Imo cryptocurrencies still needs time before it becomes mainstream.
Crypto hasn't gone mainstream yet simply because most governments don't allow it. Most of your points are valid but not major. These are just some of the difficulties crypto users need to deal with. But when it comes to mainstreaming, these reasons have very little influence (except #4).
This is not true there's more countries that accept Bitcoin than countries that banned Bitcoin.
One more thing.
Cryptocurrency is less safety compared to any other invesments.
That's why people not brave enough to invest some of their money to crypto.
While the people who already involved, get much profits.
It depends on which crypto you're investing on because not all crypto are volatile.