The original theory of Bitcoin was, as described in the paper, decentralized digital cash. But in practice it was never optimized for what normal people use cash for. As system like that would be something like M-PESA.
Even at the time, cash was declining in usage. In the 18 years since, it has declined a lot more. And for good reason, because what most people want for most things isn't digital cash, but digital money. E.g., debit cards and Venmo.
So pretty naturally Bitcoin has value only for a few niche use cases that are not well served by more effective systems. Various sorts of crime, mostly. Digital cash, sure, but the kind that's transferred in unmarked envelopes slid quietly across the table. The kind that is delivered in a briefcase.
As a side note, it also failed in its goal of being decentralized. The mining power is very concentrated. Much more so than the banking industry, for example. And most users keep their Bitcoin on deposit in centralized services. So it's again basically banking but worse.
