>why does (nearly) every organization ‘have’ to be for-profit?

The opposite, not for profit, usually means, for loss, which is not sustainable.

An organization designed to be zero net will also die during hiccups and downtimes.

So if you want something to be sustainable, provide stable jobs, provide continues benefits to whatever it serves, "for profit" means it runs on less than it makes, allowing it to survive.

Basically, all the "not for profit" things die, and you don't see them around very long.