My DH became a higher earner than me after the birth of DC (we earned roughly the same before that) but absolutely benefits from being married, and he would be the first to admit that. Essentially, being married means we can make decisions that are beneficial for the family unit, rather than me feeling like I have to look out for myself as an individual even if that negatively impacts him or my DC.
For example, if we weren't married I would have gone back to work after 4 months maternity leave (working with Americans that was all I could take really). He would have had to do 50% of the childcare and 50% of the night wakes and household chores and cooking. Instead, I basically do everything except for when he plays with the toddler after dinner. He works long hours and earns enough that he doesn't 'miss' my salary, so that trade off of me not working and him getting a better quality of life was absolutely worth it to him.
From a values perspective, both DH and I preferred the thought of DC being cared for by their DM (or DF) rather than at nursery for the first 2 years. If I was working that wouldn't have been possible but if we weren't married I would have wanted to go back to work to protect myself... So we're both living a life aligned with our values, thanks to being married. I think that counts as a benefit to DH.
Also, he wanted to move to a low tax European country. The amount he saves in tax is the equivalent to a decent UK salary. So, we save the equivalent of one decent salary in tax AND I don't have to work AND my DC is better off (not just because I'm home with DC, but also because it's a lovely place and DC will be bilingual and also living by the coast has fixed their eczema). No way would I have moved to a country where I don't speak the language if I wasn't married because I can't get work here.
Also, we've moved country twice on my DH's request (once to the USA and once to Europe) and in both cases it was 100% easier to get the visa as a married couple. Actually, I definitely wouldn't have been able to live in the USA without being married to him and therefore he wouldn't have moved there and that would have dented his earnings a lot too.
So I do think that higher earners can benefit from marriage, in theory, even if the woman is the higher earner. However, from what I read on MN when the woman is the higher earner and the dad is at home it's usually because he's a grifter and he doesn't do anything around the house and normally demands that the kids are in nursery too... and then the woman gets screwed in the divorce.. so it's a very individual decision I suppose.