Getting married to my husband didn't really change much at all. It was a great party to celebrate our commitment to each other, and deciding to take his name meant that I got the same name as our daughter, too, which I liked. But it was not the huge thing some people made it out to be.
Leaving my homecountry, family and friends behind, and having children with him certainly were the much bigger events to us.
I guess being married would mean less hassle in the event anything happened to him, or to me, but that's about it. Not sure who presents it as "the better alternative".
So I personally think cohabiting in a long term relationship is not really much different to being married, but I do not share your opinion that it sucks. Much the opposite. Moving in with my husband, and sharing a household and my life with him was - apart from having the children - the best thing I've ever done.
I don't feel as traditional gender roles are pushed on me either - apart from the fact that UK law meant that it was me who had to take maternity leave, even though it would have been financially better for us the other way round. I'm working full time again, as does he, on an equal income.
It was me who moved countries rather than him, because I speak English fluently, while his German needs still a lot of work - it was easier for me to find a job and build a career in England than it would have been for either of us in Germany, so it was a no-brainer which had nothing to do with me being a woman and him a man.
I'm aware, it's not like that in every relationship, and a lot of relationships lack equality, no matter whether there's a marriage certificate or not. But I don't think that stopping to recognise relationships would change anything for the better. I believe the way to address this is to continuously challenge stereotypes, and broadcast the message that living according to stereotypical gender roles is not the only way of living.