Btc main use case now is this:
Bitcoin is good market prices indicator to show just wich way all other coins likely will go.
If there is another reasons to use ....its unlikely.
People say specially traders that btc price is good indicator also to show wich way altcoins might go.
For payments and moving funds the stablecoins are definately best ones.
But yeah..now we know btc main usecase
Due to traders speculating the use case of BTC evolved. In any manner, it's still the use of BTC whether we use it for buying stuff as currency or use it to invest or just a store of value. It depends on how you use it, some use it to gamble. Today I think most will just buy BTC to speculate on its value in the future to make money. Buy BTC to make money.