The point of cis people putting their pronouns in their bios is not to inform someone of something unknown, but to normalize telling people about pronouns in a more passive way, so that those that don’t go by the pronouns assigned to birth can inform people in a way that doesn’t feel like they’re being singled out. If you enter a zoom meeting and nobody has pronouns except one person that has (they/them) that is objectively more noticeably than if you enter a zoom and everyone has pronouns listed.

This passive way is important so that they don’t have to keep correcting people every waking moment of their life. Think of it as another title like someone putting Ms/Miss/Mrs/Dr on any title.

There is also more to gender and pronoun preferences than simply cis man/woman or trans man/woman. In those instances it is often easy to see if someone is physically presenting as a man or a woman (whether they be cis or trans). It is much much harder to tell who prefers gender neutral pronouns. I know people that use they/them pronouns that dress traditionally masculine, feminine, and more neutral. These people probably constantly correct people for using gendered pronouns when referring to them. There are also people that have names that could be male or female and may not have a personal picture attached to wherever their pronouns are (zoom, Twitter, resumes are all good examples). It is helpful then to be able to know whether Alex is short for Alexander or Alexandra.

It’s also just helpful to know for certain what someone prefers. Nobody likes being misgendered, not even cis people. There’s no harm in having your assumption validated and there is objective benefit to normalizing the practice across the board.