Jesus Christ, if you actually took two minutes to read and listen to other people's points of view rather than whining about your lack of understanding, you would find the answer.

Those of us who choose to include our pronouns in bio's and such aren't doing it for ourselves, but for others (I gather from your writing that you may not be familiar with the concept). The more cis-gender people who present their pronouns in this way, the easier it is for trans and non-binary people to do the same.

So we are doing it with an understanding of why, there is no 'following a trend' about this. Pronouns have always been used, now it's just safer for people to consider other options than 2. Why does it worry people so much? No one's trying to make you use they/them for yourself, and it's very basic respect to use the pronouns that other people feel comfortable with. Seriously, it's the lowest level of human decency to treat people with respect, give it a try.