Bitcoin is better than cash in many ways and I think the best part is just putting your fiat in Bitcoin for some months or years and double or triple your savings without doing anything. If you have the same cash in bank or in any other investment the same cash will be just grown 1% or 2% only.
investment in banks is verry slow , you can only earn about 1% interest per year even if you put a large amount of cash. yet majority of people are still believes in banks because banks are kinda much secured and legit in any way. bitcoin is better than cash because you can do many things on it that cash cant posibly do but cash are still the choice of most people because they already knew it and every single people in the earth knows it , while bitcoin has still lack of exposure to the public.
In my country, even the interest rate of bank investment is 7-8%/year, but most of the people still choose to use money for business or buy Gold instead of saving money in bank. Depend on the banking system too much will make the world's economy become passive. Especially when you want to grow your life more, you need to working instead of saving in bank.