A central plank of the US dollar (all fiat currencies, really) is that if you hold on to them for long enough all the wealth you had when you first picked them up gets transferred to someone else.

Compared to that baseline holding literally anything else - including crypto - has a better theoretical chance of preserving your wealth. When measured in terms of US dollars, that has the appearance of everyone who owns it getting richer.

> How can any financial instrument/currency make everybody "rich", in any real terms?

You have resources, someone else has a really good idea for how to use them. Financial instruments let the situation play out sensibly (you lend them resources, get back resources + something) with easy-to-manage legal enforcement if something goes wrong.

More complicated financial instruments let that scenario play out in more abstract ways. All in theory, in practice most people are bad with debts and more complicated concepts.