And in the end, what value was created? "Liquidity in the BTC market"?
Jokes aside, it's actually something I am thinking about a lot. Such systems don't create value, but they extremely intellectually interesting and I've learned a lot. You can say the same for many other projects, for example academic research in many fields. Most of it is just noise to promote the author and does not create value in the world. But it's intellectually interesting, so people work on it.
Other people write compilers for fun to learn something new without creating value. I don't think this is fundamentally different.