Why are couples favored taxwise?

Question

Why do taxes privilege unions of two people (usually married, but also straight or gay de-facto couple nowadays)? Do you think "progress" will bring favor to other kinds of multiple unions for "affectionate" purpose, such as threesomes, etc? Especially now that the concept of "couple" is getting more and more devoid of its purpose of creating a "family" with biological children for the proliferation of the human species?

Answer 1

Because they form a society

Societies are "better" for tax purposes.