I sort of wonder why people bother marrying in that case. Although even in our case procreation was only 50% of the reason and basically doing a big thank-you ceremony to our parents was another 50%, we felt we owe them a wedding. But I think this is related—the wedding as a thank-you ceremony is a signal of the end of childhood to parents (at 34 it was about high time) but also a signal that we will take over the mantle of child-raising from them from now on, now we take over the job of continuing the family for them. So it had a bit if retiring them as parents, and we do the job of being a parent and doing the duty to the family now. (Nobody actually called it a duty, but it still felt like one generation stepping in the role of the previous one.) So the idea of “thanks parents your job is over” and “we do it now” was related.
I sort of wonder why people bother marrying in that case. Although even in our case procreation was only 50% of the reason and basically doing a big thank-you ceremony to our parents was another 50%, we felt we owe them a wedding. But I think this is related—the wedding as a thank-you ceremony is a signal of the end of childhood to parents (at 34 it was about high time) but also a signal that we will take over the mantle of child-raising from them from now on, now we take over the job of continuing the family for them. So it had a bit if retiring them as parents, and we do the job of being a parent and doing the duty to the family now. (Nobody actually called it a duty, but it still felt like one generation stepping in the role of the previous one.) So the idea of “thanks parents your job is over” and “we do it now” was related.
Off the top of my head, some reasons why people would to marry despite intending not to have children:
residence permits
taxes (a pretty big deal in some countries)
warm fuzzy feeling about cementing a very-long-term relationship in the culturally approved way, signalling commitment
doing the culturally expected thing in a very-long-term relationship and not wanting to advertise their child-free status
Or in some cases, “yes I am serious about this stop giving us these looks already”.