There are some limitation which stop bitcoins from being used as a currency. For instance, the transactions are not instant and it is a big limitation in my opinion.
Bitcoin on-chain transactions are not instant but that's why we have Lightning Network which allows for instant and extremely cheap payments. It is not perfect solution, you have to know how to use it at this moment because there are not many users there. However we are on a good way to make Bitcoin more popular.
Bitcoin is an easy way of sending money around the world within seconds while the banking system is not frictionless like the Bitcoin as here you click the button and there the amount is received. Banking has holidays and some technical problems some times while internet is always active and we can transact through it in Bitcoins which is necessary and we use it as a currency.