I'm not kidding, everyone should have pronouns in their bio. Yes, even if you're cis. Yes, even if you're famous and everyone knows your gender already.
Because addressing people the way they prefer is just basic decency.
You wouldn't call Ashley “Samantha” just because you like that name more or because “she looks like a Samantha to you”. Or even if she does have the name “Samantha” in her birth certificate but she absolutely hates it and prefers to use “Ashley”.
And it's the exact same story with pronouns – if you don't want to be rude towards someone, please address them properly. The only difference is that we usually know names, but not pronouns. We introduce ourselves with a name, but not pronouns. Let's change that
Because gender ≠ expression ≠ pronouns.
There's people who look manly while being women (either cis on trans), there's he lesbians, there's nonbinary people using binary pronouns for different reasons, etc. etc. Seing a picture of someone's face doesn't automaticly mean you you'll be right when you assume their pronouns.
Because it normalises doing so.
Sharing their pronouns is very important for trans, nonbinary and gender nonconforming people. Alas, it also exposes and singles us out. But if cis people do the same, it means the world for us. It makes us feel more confortable, safe and welcome.
Because it shows support.
Even if your friends or fans know very well that you're a cis man, adding this “he/him” to your profile still gives them a very important information – that you support the trans community and those struggling with their gender identity.
Your support is important. Especially if you're well known and influential.
Because it reduces confusion.
Talking to someone who looks androgynous and you don't know how to address them without offending them? Normalisation of giving pronouns and asking about pronous comes to rescue!
Because it's positive and harmless.
Seriously, there's just upsides and no downsides.