> I don't know what it is with a certain class of people who need to explain everything in reference to straight men.
> these same people would explain that due to straight men: "Because heterosexual men have penises, representations of penises are celebrated and glorified..."
You are setting up a bit of a weak man fallacy by presenting it this way without evidence, but I imagine there probably is cognitive dissonance around this (and other topics about men).
Partly, I think it's because there are no groups that represent or advocate for men. This hypothetical group, in the current cultural climate, could be hijacked by bad actors or other identity groups, or it could result in an even more monolithic or myopic view of men than exists in pop culture today. Such a group would need to be prepared to deal with these issues without being exclusionary, divisive, or dehumanizing. I think this challenging and would take all the right people to organize such a group.
Identity based groups tend to project a monolithic image of people that is inaccurate. For instance, if you browse the internet long enough you'll probably develop a fairly myopic view that lends towards some -isms that certain groups have, however, if you talk to people in different cultural regions you'll likely discover that what large groups represent is largely in-contest.
Edit: the earlier version of this comment confusingly stated that there's "good reasons" that these groups don't exist.