Comment by NoboruWataya

Ultimately, they are governments, businesses and individuals. All of these actors regularly face situations where they need (or want) to expend money now that they will have eventually but do not have now. The financial markets are primarily about making it as efficient as possible to do that. (There is arguably another side of the financial markets that is about helping people manage risk, though they are somewhat related.)

Most of the financial wizardry you read about in the linked article is related to that aim. It's not always obvious, because a lot of it is higher-order stuff: transactions between financial market participants where payouts are linked to other transactions (or aggregations of transactions) between financial market participants, etc. It can be hard to see the link to the participants I mentioned above. But a lot of it is a means to understanding, and spreading, the risks associated with financing those participants. It is a lot easier to lend people money to finance their wants and needs if you can (a) differentiate between people who will pay you back and people you won't; and (b) share the risk of not being paid back with others.