Many people have terrible social skills, and introspection.
There’s also the issue that many people choose mates because they want to have sex with them, or because they were young, or gave them attention, or were just around (or some combination of all these things).
People are awful at choosing long term mates and the discussion around this and the selection criteria is really bad.
If your partner has core value differences or just isn’t at some threshold of general intelligence the relationship will be filled with this kind of anxiety inducing misery.
This goes both ways too - I’ve known brilliant women who dated oafish/dumber, but very good-looking/fit men that were filled with similar insecurities. People should select more on core value alignment and intelligence than they do.
The brainwashing isn’t some secret truth of spousal relationships, except perhaps that people are bad at long term mate selection and select for the wrong things.