Its mostly a question of where to spend effort; In the same way I'm probably not going to read a paper with a shoddily written abstract, unless external reasons apply (ie the paper was recommended to me by someone trustworthy), it doesn't make sense for me to try to parse a shoddily written resume.
It takes more effort to do so, and its nonsensical for the person not to put effort into it, because its only written once ebery few years, and because its the first point of contact.
If you're going to operate at the level of a tenth grader, why would I assume you have anything more to offer than what a tenth grader might?
Of course the metric might fail, but hey, there's a hundred other resumes to have to go through too, and you managed to imply you're incompetent right off the bat, so I'm probably better off looking elsewhere.
Theres also the aspect that I personally don't want to put up with shoddy writing, and also the fact that these are not long documents. Its like 1-3 pages half-sentences and spacing everywhere; I'm hardly asking the world of you by requiring you bother verifying what you write.
>But at the same time, why the hell are you judging the suitability of a professional in a complex technical field based on typos in something they only write once every few years
Because, with the exception of some rare positions, there are a lot of people suitable for the job. There are also a lot of people who will apply without being suitable. And a lot of the people who apply at random, aka sloppily, are presumably also sloppy about the rest of the process.
So filtering on sloppiness is probably a decent utility; of course it'll remove the sloppy suitable candidates, and it won't remove the non-sloppy unsuitable candidates, but hey.
Alternatively we can do modern hr stuff like filtering resumes on key-word searches, so if you're an expert in Oracle 11d but not Oracle 11e....
Every filter is fucked somehow; but typos seem to me one of the least fucked, precisely because its so easy to avoid. You only write it once every few years.