tl;dr Gender-neutral pronouns should be easy to pronounce and recognize.
World culture is changing. People are now able to express themselves in non-binary ways. We now document everything, theoretically forever. It's easier and easier to be anonymous. Because of all this, we need a way to refer to people without assigning a gender to them.
The popular choice is to use "they" and "them". The problem with this is that it's nonspecific: It denotes a plurality, so it's not intuitive if one is referencing an individual or a group. A common argument for these is that William Shakespeare used them in his works. However, there are two distinct problems with this argument: The language was very different back then, and many of the words and phrases he used have since been discarded as part of his time period; There was no alternative available to him, and using a new term would confuse the audiences and distract from the captivation and immersion he carefully built.
|Subjective||Objective||Possessive determiner||Possessive pronoun||Reflexive|