Your point is a very strong one, but I do think there’s a distinction to be explored between the decline of marriage itself and the rise in those trends. As you allusion to, there’s a real question of the causal relationship here. The strife between the genders in particular seems unlikely to be fixable through an increase in marriages, all things equal.
I suspect the underlying issue is social media and the shift away from many in-person interactions. The echo chambers people find themselves in are major drivers of anti-social behavior and rigidity, and I think romantically relationships form easier with proximity and physicality that is hard to mirror online. There’s a sense of ease I feel just being next to my wife sometimes, and there are so many subtle moments in expressions and tone in the course of a relationship that are not replicable online. We’re more connected than ever, but I think some of that added connection is harmful to this particular type of relationship.
Once that first domino falls, I think it becomes a genuinely slippery slope. If you’re not able to communicate and compromise, you’re just going to re-enforce your own assumptions and grow lonely and bitter.