Are you okay having the tables flipped and someone calling you “sis”?
Using male language as the default may not bother you and you may have no ill intent with it, but it does have a history tied to it. A history where women were seen as less than and didn’t have equal rights. Western society still uses male language slang regardless of gender (hey guys, dude, bro, bruh) and it all stems from a history of a patriarchal society. Every time we say, “hey guys” to refer to a mixed-gender group, we perpetuate patriarchy, whether we intended to or not.
Legally and overall culturally, women are still seen as less than and we still don’t have equal rights (e.g. divorce and abortion law).
If any minority group was being systemically oppressed, I would absolutely love if the shows and games my children were into included messaging of the problem and how every human is inherently equal.
And you may think your wording is hyperbole, but trans people are actually being exterminated in parts of the world and imprisoned in others, and are actively having their rights and legal identities taken away in the US as well.
People upset about seeing trans messaging are the same people who would say “i don’t care about people being gay but stop shoving it down my throat” when they saw one gay couple kiss on tv that month while also seeing 100 straight couples kissing.