but the only reason it exists is to be used as a currency. If none saw it like that, it wouldn't have a purpose to be an asset.
People invest in things for their future usage. In this case, they invest so that one will use it as a currency in the future.
It was created to be an internet currency. Satoshi made it that way. But after a decade it found a different, much stronger use case. History knows lots of inventions that was ment to do something but after a while someone found better/different usecase for it. Bitcoin is one of them. Stable coins on fast chains like TRX or BSC serves much better as internet money than bitcoin. I pay/recive payment almost every day. Most deals are made via BEP-20 BUSD. But am I holding it as BEP-20 BUSD? No, because I dont trust it. Its fast and easy to deal with but not safe to store wealth for more than its needed. So I transfer value to bitcoin to store it there. Especially if price goes down and we are far from ATH.
I don't think that investors buy bitcoin in 2021-2022 because they bealive its going to be used as internet money in future. They did that in 2009-2017.