Most people don't have to care about pronouns. For a small subset of people the gender of their brain does not match the gender they appear as. Passing as your preferred gender can take years and is mostly down to genetics. So non-passing trans people will ask others to use their pronouns so they can socially transition before they pass. And that isn't even mentioning non-binary people. The reason cis people specify their pronouns is to normalize it for trans people who don't have a choice.
Most people don't have to care about pronouns. For a small subset of people the gender of their brain does not match the gender they appear as. Passing as your preferred gender can take years and is mostly down to genetics. So non-passing trans people will ask others to use their pronouns so they can socially transition before they pass. And that isn't even mentioning non-binary people. The reason cis people specify their pronouns is to normalize it for trans people who don't have a choice.