Banks have an obligation to pay out that money to you if you want to withdraw it. If they can't, they may face legal consequences as well as lose credibility and many people will want to take their money and put it in another bank. That number has real power.
Something just being online vs. not... that on its own doesn't make a difference and I don't think anyone claims that it does. If you think someone here has claimed that then you don't understand what an NFT is in the first place. An NFT is not something that has any intrinsic value because it's nothing more than a digital receipt in the form of a little bit of code. You can't do anything with it other than sell it again for some other currency. Since it's not anchored to anything meaningful like actual currency is, the only worth it has is the worth you can convince a potential buyer that it may have in the future.
Now, you may think that there's some kind of value in owning the thing the NFT is attached to, whether that be digital art, a chess game, or something different entirely. That's unfortunately not true, because in the digital world everything is fungible by default. There is only one Mona Lisa but a digital artwork is just a string of ones and zeroes that can be sent all over the internet at a moment's notice and sit on the computer of tens of thousands of people. The token that says who owns the image may be non-fungible, but there are easier and more effective ways to accomplish that, such as the artist revealing who commissioned their work, and watermarking it so it can always be traced back to them. The only reason you might want an NFT instead is because you're interested in trading it rather than in owning it, which once again goes back to having to convince any potential buyers of its future worth, and once again it intrinsically does not have any.
Nobody believes they're the common man. I'm me I'm special. I'm worthy of being ripped off.