Not thinking about the value of it, but of its future usefulness as value store and as mean of payment

I don't believe you can separate the value of Bitcoin and it's usefulness because the more valuable Bitcoin is, the more useful it becomes.

The more people who hold Bitcoin, the more scarce it becomes and therefore the more valuable it becomes. In 20 years, Bitcoin could go to 0, or become a widely used currency and skyrocket in value.

Once the number of Bitcoin holders reaches equilibrium then the value would remain stable, but we are definitely not at that point yet.

For the simple reason that it exist in the physical space and can't disappear, unless the laws that regulate our existence change, which is quite improbable

Gold will also work and retain a value even if society suddenly shuts down and reset to a "sticks and stones" state

Bitcoin advocates have this weird tendency to completely ignore decades of game theory

That's why people don't trust them

I doubt this is true in every case, maybe even most cases. Though this sentiment does seem to become more rigid toward the core of the crypto community, a huge swath of other investors are playing price action. There are tons of technical traders in crypto, and they tend to care much more about MA deviations, gaps, pennants, and candlestick forms than what's going to replace USD.

You can also think of it as a play by (people who don't have as many concerns about the dollar) off the fears of (people who are afraid about the future of the dollar).

IMO there is a lot of room in a speculative ecosystem for non-value, non-traditional-economics, and even hugely irrational viewpoints. They can all meet with success by using their own sets of strategies.