You do understand that the compromise is that everyone is free to call their relationship marriage, and that gay and straight couples would both enter into a civil contract that has a different name than
marriage?
A word only has a meaning insofar as a culture decides to use that meaning. So yes, the preferences of individual members of the culture taken collectively are by definition relevant to the debate.
So hopefully we can agree that the current definition of a word is solely about preference.
We are having a problem coming to a consensus over the meaning of the word "marriage."
Group A says it means "one man and one woman"
Group B says it means "two people"
Group C says it means "any group of consenting adults"
If you are in Group A, using the word marriage in a legal document, in the context of "any two people", means you think the government sides with the preferences of Group B, and vice versa.
Two (or more) sides disagree, so a compromise is proposed--we don't use the contested word, we create a new word that everyone can agree on.
Imagine if 2 groups argued about the definition of the word "planet."
Group A says a planet "is spherical"
Group B says a planet "must clear its neighborhood"
The governments starts using the Group B definition, but almost half of the people still use the Group A definition.
In order to avoid a huge fight we compromise and come up with a new word that includes objects that fit both definition, solely for use in legal documents.