There are many, many people whose only understanding of manhood is through defining it by its association with power.
Whether that be through a feminist lens regarding manhood or masculinity only through the analysis of cis patriarchal hierarchy, and/or an uncritical repetition of gendered norms produced by such a system.
So what ends up happening when a transgender man explains he is disempowered, and disempowered specifically in relationship to being a man and how the ideas (just like this) attached to it effect him, the only conclusion they can come to is that he must be implying he isn't a man, that he is misgendering himself or undermining his identity, or that he is weak and failing to live up to it- or that he is lying.
The complicated marginalization of trans manhood as manhood is so radically contradictory to the patriarchal values of power which men are expected to fulfill, and so contradictory to the intensely cis-normative approach to feminism and gendered oppression, that his experiences end up in a placeless void of compounded invalidation. Although coming from the very same place.
Enough that to even have acknowledgment for his experience of gendered oppression, his identity as a man must be severed from the very context of its existence. Just transgender, just a generic, unspecific transphobia. Denying the specific modality which produced the reality of his transgender existence. Cutting his social experience into pieces, either cutting out the manhood, or cutting out the weakness.
This continues on his invisibility, furthering the doubt of the validity of his own reality. Feeding into the inevitability that his struggle will go unnoticed and uncared for, and will not receive the attention needed to help him, or to change these things.
Ironically and integrally, all of this enabling his marginalization specifically because- well because he is a man.
Because of the expectations of what it means to be a man, and how we cannot imagine his experience of a specifically marginalized manhood.