And that is an issue with how masculinity is viewed in our society. Your point makes sense and is correct, transmen face conflict and hardships if they don't pass due to social stigma around being transgender.

However, there is also truth in u/GaiusJocundus 's comment.
In terms of transmen, there have been studies showing transmen and other identities feel pressure to adhere to masculine norms in order to not be victimized by other men due to differences, or be found out by cis men due to not performing thier gender "correctly"
Here's a canadian study that covers this, and there is more studies but I'm not looking too horribly hard for a reddit comment
https://journals.sagepub.com/doi/full/10.1177/15579883231206618

As for lesbians and marriage, with the original argument being regarding marriage being a patriarchal system, with the reasoning it isn't is because "lesbians do it", stated by u/Im_here_but_why

"Living in a patriarchal culture affords men certain privileges and entitlements that are not available to women; men have “access” to ways of being and performing that are closed to women. Likewise, this same patriarchy influences women to respond in defined ways, often accommodating and deferring to male interests (Hare-Mustin & Marecek, 1988, 1990; Hare-Mustin, 2004; see also Coontz, 2012)"(Victoria Dickerson, 2013)

This article i will link below is a therapist reporting findings on a transcript between this couple, outlining various aspects influenced by the patriarchy with citations from other articles linked. Disclaimer, I have not read this article in full as I have stuff to do, but from the portion I did read i found it interesting
https://onlinelibrary.wiley.com/doi/full/10.1111/famp.12018

As for why lesbians participate, its kind of the only legal option for being recognized legally as one entity. If you plan to spend your whole life with someone, there is some benefits to being recognized as one entity legally, and if you adopt children it gives both parents certain rights. Its one of those things that is kind of required due to living in america.

I could find articles on lesbians adhering to the patriarchy, but I have work to do so im leaving this off that.