[dragonwriter]

That's "simpler" in the "fewest number of base rules" sense, and more complex in the UX sense.

Given the frequency of the desire to enter into a partnership with something like the kind of mutual exchange of commitments and agency relationships packaged in civil marriage, it makes sense as a UX optimization for government in terms of providing sensible defaults for common needs (with the ability for users interested in different configurations to reconfigure the defaults to a certain degree.)