I haven't used bitcoin to purchase anything,and I would like to purchase goods with bitcoin some day.I prefer using fiat to purchase things both physical and online because I wouldn't want to tamper on my holding.Though the main purpose of bitcoin is to purchase goods online and prevent double spending,but now it's more of a store of value than a payment method.The only reason that can make me purchase something online with bitcoin is when there's no fiat in the payment option otherwise I prefer payment with fiat then
my bitcoin for investment purpose.Outside the internet,many countries are restricted from transacting bitcoin in public,so that also be among the factors why Bitcoin isn't used as a payment method.
The reason why most people prefer using fiat to purchase goods online and physically is because not everybody knows much about Bitcoin, most of the people purchasing things with Bitcoin, and up to now, there are some countries where using Bitcoin is still illegal. That’s why even those that know about Bitcoin are afraid of purchasing goods with it.
The way the fiat is even devalued in some countries is why we can see most of the country using the bitcoins for the transactions, because it reduces spending a lot of money, and it also makes the transaction come easier and faster for people who want to buy goods online.