It is true that bitcoin is not used for mode of payment but as investment but it is what the decentralization and freedom is all about, we get to choose what we want to do with our money with fiat it's what government wants even though we worked and earned it. Also we lack the infrastructure to use bitcoin as currency which may take a while for the transition to happen until that accumulation is the best way to ensure better future not just in terms of returns but also to power shift from centralized banks to the individuals.
Bitcoin was created solely as a payment as pair to pair but you know one thing is to create something and another is for people to use it for different purpose. The demand and the supply create value in Bitcoin and since many people see true value in the price of Bitcoin, they tend to use their fiat money to buy Bitcoin instead of holding fiat that lose value with time. Over time, Bitcoin has proven to be store of value than pair to pair transaction payments.
Almost everyone you see today use Bitcoin is solely because of that store of value, even the institutional investors are here for the store if value. If really they are after payment method then I think Bitcoin is very poor when it comes to transact payment, things like Visa has that speed to process the speed of transaction but the down side of them is because they are centralized while Bitcoin is decentralized, nobody can disrupt your payment from reaching the other side.