To me, those things are implied by the "non-betrayal" stance. Agreement on childbearing, shared financial interest, and pair bonding (i.e. shared emotional interest) are consequences of the fundamental agreement not to betray. As you note, each of those could be achieved without marriage - but most people act as if this were not possible. I'm just as confused as you.

That is different from noting the incidental benefits of legal marriage - if I die without a will, my wife gets my property. To achieve the same effect without marriage, I'd have to actually create a will. And so on for all the legal rights I want my wife to have (e.g. de facto legal guardian if I am incapacitated). But I want my wife to have those rights because of the non-betrayal stance, and if that wasn't our relationship, I wouldn't want her to have those rights.