The difference is that banks almost guarantees the profits that they are promising, while with Bitcoin no one guarantees anything, you can earn a lot or lose a lot. Also banks serve another vital function - they lend money to people. Because of this, banks will always exist.
If you imagine all people in the world abandoning their saving accounts for Bitcoin, it would create an enormous bubble, and the early buyers would profit from it greatly, while the late buyers would lose everything, as Bitcoin would correct by 95% or more. This is just a thought experiment, because nothing like this is going to happen, but still.
and if i may add, with savings in the bank, you know for sure that your money is safe and secure and will not lose its value overnight. though the interest is really small as compared to other financial investments, but you can also get other benefits by keeping your money at the bank like if you want to lend in the future. just treat it as someone is securing your savings.
with bitcoin, you can really get very good profits these days. however, what if the opposite happens in the market? i guess you will tell to yourself that you should have kept your money at the bank.
so this situation goes to show that there are really advantages when you diversify your portfolio, you can get both the benefits of these types of investments