When your marriage is not legally recognized, you can't utilize many of the legal benefits of that marriage. For instance, hospital visitation, medical authority, and many things along those lines.
As for "entitlements" perhaps you refer to things like married people being able to transfer their homes to their spouses so that it isn't attached by Medicaid when they get sick in their old age. Entitlement? So what you are saying is that only heterosexuals are entitled to "entitlements" like those? What makes you think so?
Governments purpose in encouraging marriage is to increase the number of children born into homes with the benefit of both their mother and father present to provide and care for them, as opposed to the alternative of one or neither of their parents present to do so. If you want to give those benefits to two gay guys who rub genitals, you really have no justification for denying the benefits to any two people who would desire those benefits. Nothing special about being homosexual, that would justify such discriminatory treatment. Society, culture, tradition, religion and law hasnt encouraged men and women to marry, for as long as human civilization has existed, because men and women have sex. They have instead done so, because when men and women have sex, children are frequently the result. Two guys doing each other in the butt, never going to happen. From BC Roman law
Mater semper certa est ("The mother is always certain")
"pater semper incertus est" ("The father is always uncertain")
"pater est, quem nuptiae demonstrant" ("father is to whom marriage points")
as it is today
§ 160.204. PRESUMPTION OF PATERNITY.
(a) A man is presumed to be the father of a child if:
(1) he is married to the mother of the child and the child is born during the marriage;....
None of this has any applicability to two people of the same sex because,
"matrimonium is an institution involving a mother, mater. The idea implicit in the word is that a man takes a woman in marriage, in matrimonium ducere, so that he may have children by her."