But then what happened to it?
wtf?
do...do they know...how many manhours could've been saved...?
Nothing happened to it. It gets used by front-end developers every single day. I personally can't follow the CSS complaints. It is easier to learn than any other front-end dev language in one's toolkit.
Yeah, everyone did a really bad job of evangelizing absolute centering back in the day, leading to lots of angry Web developers and awful hacks like the inline-block/vertical-align trick. It should have been the first example given for "position: absolute"…
That standard exists. It's called flexbox. It was designed to solve exactly this problem (among many others), and does.
That said, as I never tire of mentioning, vertical centering was a part of the design of CSS 2.1. The technique is called "absolute centering". See CSS 2.1 10.6.4 [1]: "If both 'margin-top' and 'margin-bottom' are 'auto', solve the equation under the extra constraint that the two margins get equal values."
[1]: http://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-hei...