To pay anyone with fiat electronic, you first need a bank account of some description, which usually means visiting a bank in person and taking a bunch of personal documents along with you, or scanning in a bunch of personal documents and sending them off to the bank. Then you'll have to wait a number of days for it all to be approved. Then you'll have to deposit some fiat, which again will take a number of days to clear. Maybe you then need to open a credit card account on top of that bank account, or similar. More KYC and more delays. With bitcoin, you can open a wallet and load it with coins in the comfort of your own home without risking any of your personal information in 10-20 minutes.
Moreover the bank accounts doesn't open easily as for this you are required to have all the mandatory documents like the address proof and your birth proof also for which you have to submit various documents which is indeed the KYC these banks do in order to have more tight control over you and you are having zero privacy but still talking about convenience?The main problem at this time is people are not using bitcoin as payment currency but more of a investment tool to earn profits in long run and we are seeing less people using it.Although we have layer 2 options like LN in bitcoin with increased btc capacity over time but still many uses other sources to pay but there are also less merchants accepting it But I am also of the view that if you use bitcoin it will be much useful with full control over your funds and it's far better then fiat mode of payments.