BTC is obviously a real alternative currency to fiat, a decentralized and censorship resistant currency, however, it is also an attractive long-term store of value, so on that note it is more convenient for most peoplr to spend their fiat that is constantly devalued by inflation, rather than their BTC that is a store of value.

However, i would not mind spending my BTC if i get the opportunity, but it would not be on something too expensive, just a few hundred of dollars, but surely not on something that costs thousands of dollars, i'll use fiat for that.