Think of it this way. How many people on earth can't easily get a bank account (people under the age of 18 included)? It's a huge number that suggests massive scale in that use-case alone.
What about wealthy individuals that want to divest some of their wealth from the influence of nation states. When a country struggles that has direct impact on the currency and we're seeing that even in the US as the money supply increased 22% last year and will be up to 40% with the recent stimulus. This also isn't just and issue with the US. I think it was Belgium (?) that recently reported negative interest rates. Countries have also started divesting away from USD in their reserves since Trump was president. So this is a real concern that people/governments have that this offers a solution to.
BTW gold doesn't solve this because when you buy it it's being held by someone else, whom is tied to the country it resides in, and you're back to square one. Even if you were to buy it physically and keep it in your own safe you're still stuck with the same problems because it's not portable. Bitcoin is portable.
