So, obviously, a lot of posts about how Sam or Dean take on a wifely role are just silly little jokes without much deeper meaning, but sometimes people make those claims more seriously, and in those cases I think it is really interesting to look at what it is that makes people percieve a character as taking on a traditionally feminine role:
When people compare Sam to a traditional wife, they tend to do so through a view of gender-as-power. Sam is feminine because he is feminized by others; he is (both jokingly and very seriously) reduced to being other people's "bitch", he is constantly violated, robbed of autonomy & socially controlled. In this analysis, Dean tends to become the patriarch of the family because he is the decision maker, the one who disciplines, the one who ultimately decides the rules that the other members of the family have to follow.
When people compare (adult*) Dean to a traditional (house)wife, it's commonly through a view of certain personal traits as inheritently gendered. Dean is feminine because he enjoys to cook, to care for Sam when he is sick and because he likes "nesting". It's not even really about the fact that he does more chores, it's that he gets more happiness out of doing them. His percieved femininity has nothing to do with power or his relationship to others; it is simply a private, personal trait, decided by how much satisfaction he gets out of doing domestic chores.
Which, like, as someone who works within the field of sexuality and gender, is very interesting because it represents to quite different, but popular views of femininity.
*in discussions of them as kids, you are more likely to see a gender-as-power analysis for both Dean and Sam (probably because John is such a strong patriarchal figure).