Crypto is also accepted as a means of exchange. There are plenty of merchants willing to accept it as payment, but they are just not geographically concentrated in one location like banknote-accepters are. With a banknote, you have a very high concentration of merchants who will accept that as a means of payment in one geographic area (i.e. the country or region whose central bank issued that banknote), while it is not accepted anywhere else. With most cryptocurrencies, they will be acceptable worldwide, but the concentration of people willing to take it in any given geographic area is low.

It is important to note that you can't take properties of the smaller coins (the ones which you are probably thinking of are derisively referred to as "shitcoins" and most are deserving of that epithet) and apply them to every cryptocurrency. Just like you can't use properties of the Zimbabwean dollar to smear all fiat currencies in general.

Bitcoin transactions on its Lightning Network are typically instantaneous, and fees are lower than most credit cards (usually on the order of 0.1%). An on-chain Bitcoin transaction currently has a fee of about 1 USD, which would make it competitive to credit cards for transactions greater than 40 USD. Bitcoin fees, despite being notorious for being the highest among all cryptos, are actually very competitive with most traditional payment methods. This transaction from the most recent block at the time of writing paid about 117 USD to move over 411 BTC worth 48.5 million USD. That means they paid about 0.00024% in fees and this is the highest-fee transaction in this block (meaning they paid the highest fee rate of any transaction in this block). The going rate for this block was actually much lower; whoever sent this transaction overpaid by about 50 times.