Spud, people live together and are quite committed, even without legalising their relationship. Ask anyone who has split up with a long term partner how traumatic the break up is and you will find it is much the same as if they were married. The difference is they don't have to pay for a divorce (which is expensive, the court fees alone cost over four grand), but that is probably the smallest consideration at the time of breaking up. There is little difference from what i can see. They share property, car, lifestyle; breaking up is very hard so don't tell me it's done lightly.
There are exceptions of course: you do see people rushing into relationships which break up quickly but in the past, they probably would have rushed into marriage and broken up quickly, which makes everything far more difficult - especially for young people. Let's face it, who would want to be twice divorced before the age of thirty?
One in five couples marrying nowadays have a child or children too so they have made a commitment. ( The CofE incorporates the children into the wedding service. )
You may not like any of that - you don't have to - but don't tell us the above people treat their relationship lightly or that making public vows would make much of a difference.
During my insomniac night, I looked up marriage in the Anglican church and found it to be, on the whole, quite accommodating to most people.
This is what is said about SSM:
https://www.yourchurchwedding.org/article/information-for-same-sex-couples/Well, we know the vicar cannot marry a same sex couple but, from what the above said, an unauthorised, ie informal or own-words ceremony, can be performed in church at the discretion of the minister. In the first place, I would think a committed same sex couple, who were Christian, would choose a church that was sympathetic to gay partnerships and give the 'antis' a wide berth.
That is progress, Spud, and there will be more in the future but it takes time. The Church does not want to alienate anyone.
Even in the Catholic Church, Pope Frances is slowly trying to alter established thinking about marriage which is upsetting the Traditionals atm, but he is at least meeting people where they are now and showing some love whereas, previously, they would have been left out in the cold.
But - none of this matters for non-believers and we cannot impose religious constraints on the non-religious, or judge them.