Due to some elements of the collective identity, we default to a lot of headmates whose default pronouns would be some combination of he/him, they/them, or it/its. The thing is, we have so many headmates, including ones with similar genders dating each other, that it can sometimes get hard to follow a conversation about our system when it's not clear what person is being referred to by which use of a pronoun like "he" or "they".
Therefore, a lot of us choose to use neopronouns like ey/em, ae/aer, or zi/zir in addition to "traditional" pronouns like he/him, she/her, or even they/them and it/its (to some extent of the word "traditional").
When talking about similar-gender friend groups or gay couples within the system, we find it genuinely helpful for clarity to be able to use a very specific pronoun for everyone involved in the situation. It also keeps some sentences from sounding repetitive or confusing due to repeatedly using "he" or potential unclear uses of "they" or "it".