This one is really the only valid reason, otherwise you're not comparing apples-to-apples.
You (most probably) did have to go (physically) to a bank and prove your identity and your credit record in order to maintain any credit card. And it takes days to wire money to your bank account. If anything crypto exchanges are trivially easy to use in comparison and you can convert one (usable) cryptocoin to another much faster and easier than any bank will allow you.
Price fluctuations are a problem, but not if you keep your main balance in a stablecoin and only convert at the time of purchase. And a crypto wallet doesnt grow in physical no matter how many different coins you store in it.
In reality, if cryptocurrencies weren't actively being fought by governments and banks, they would have conquered the world in no time because they are so damn easier to use and secure.