They were already equal under the law!
Did you know that farmers get money for farming from the government? So where's mine? I don't farm, but dammit equal protection!
No, I don't get free money from the government for farming unless I actually farm.
It's the same way with state-defined marriage. The states didn't establish a right, they established a subsidy. A subsidy for people to have sex. The reason states were happy to grant this subsidy was generally people having sex produce children. More children, more people, more commerce, more chances for taxes.
So in exchange for expansion of their future tax-base, states afforded tax breaks and other incentives to get people to commit to creating and raising little future tax-payers.
Thus gay persons were already equally eligible for this marriage benefit -- if they were willing to marry the opposite sex. Obviously this was not an acceptable requirement for gay people who wanted the subsidy and other incentives associated with marriage despite their natural inability to reproduce as a homogenous team. Well, there were heterosexual exceptions with marriage so:
Redefining marriage to include sex-acts that generally don't produce children was a bet some states thought was worth making. So they did. But now SCOTUS has decided for ALL states they must include homosexual unions as an exception -- the same exceptions they make for sterile and old people.