A lot of rich people use Bitcoin for self-realisation (e.g. to get that special "I own a lot of Bitcoin" feeling). As an average person, you might think it's a ridiculous use case but it's actually very important to them, therefore it's very important full stop.
It's the same reason why fine Art is expensive. People want to experience a very specific "I own a Picasso" feeling.
Normal people don't understand this, but what normal people think doesn't matter in the current economy.
Okay, so in addition to that claim being unsupported and rather unlikely you have a major problem with this theory: art only requires one person to like it but a currency requires an active network and someone who just likes to look at SHA hashes isn't going to generate much transaction volume.
Well there are a lot of technology-oriented rich people who want to be able to say to themselves and others that x% of their wealth is in Bitcoin (even if it's just a hedge bet) and this shared desire to own Bitcoin is reliable enough that it can be quantified; and that shared desire determines the market cap of Bitcoin.
It's not different from any other currency. The main difference is that a government cannot use the tax system to force people to use Bitcoin - But then again, the government cannot force rich people to pay tax at all.
It's the same reason why fine Art is expensive. People want to experience a very specific "I own a Picasso" feeling. Normal people don't understand this, but what normal people think doesn't matter in the current economy.