When Magat's go one about when "Murica was great" they are simply referring to a time when things where much easier for white men, as a whole.
Fact is compromise in marriage is hard. In the 'olden days' men did not really have to compromise. It was up to the woman to conform and 'make her marriage work', even if he was a drunk abuser as the cost to women was so very high in divorce, as i point to upthread. That is why when you saw so many of these 'great men' given life time achievement awards and speaking, near the end of their lives, they would talk about 'what a saint' their wives were for 'putting up with them and making the marriage work'. No, not all men, were drunken abusers, but if you were those were the 'great' times as your wife would suck it up and stay with you.
Now you have two people, as both partners need to find compromise, and that is very hard, thus the divorce rate. Think about like work. If employees have the exact same power as bosses, suddenly it is much harder to keep employees.
Aspect 2 is now those same white men have to compete with minorities and women for the upper tier jobs. America was great when all those spots were reserved for them. And even if, you did not get an upper tier job, as a white male, at least the women and minorities would not have them either. That kept the white male value much higher for women, few of which who had any path to independent living so even pairing with an average earner male, was a big deal. Now it is harder as women have more choice, and many minorities are doing much better, making many of magats feel inadequate.
So MAGA harkens back to a time white males saw as ideal, because it was easier FOR THEM alone and life with out competition from any others (women or minorities) means you are winning even when you are not winning.