The first written instance (that we know of at this time) of singular ’they’ appeared in the book William and the Werewolf. This was an English language version of an earlier French work called Guillame de Palerme. It was commissioned by Humphrey de Bohun, 6th Earl of Hereford, and written by a poet known only as William in 1350. So, during a major historical event known as the Black Death.
Also - do you, Oh Mark Wiering, 0th Earl of Nothing at All, use the word ’you’ to convey second person singular? Because according to grammarians in 17th century England, you are a fool or even worse… a Quaker.
Language changes, dude. It evolves. I’m sure you (ha!) use plenty of words that don’t mean what they used to. I highly doubt it’s confusing to you, this is just plain old tap water queerphobia and misogyny. Because what word used to be the only *“acceptable” generic singular? Oh yeah, **’he’. Get over yourself.
*publishing houses and grammarians knew that they was an available option, because people were already using it colloquially and clearly had been for some time.
**I credit this trend with at least some of all-around acceptance that women don’t do anything of note or contribute to society. For if we hear only the word ‘he’ or ’him’ or ’his’ when denoting the average non-specific person for our entire lives, it affects our psychology and erases other genders from our thought processes. However, ’they’ and ’them’ aren’t associated with gender, and that I think is a big part of what pisses these people off about it. And of course the enbyphobic garbage.