If brevity is good, why must I write long papers?

A recent quote from a fellow jelly: The truest measure of a writers talent is their ability to keep things succinct. Writing a 600 page novel is time consuming, but it’s nowhere near as difficult as summing up that novel in a 3 paragraph query letter…. Verbosity is the enemy of specificity.

So if this is true, then why are students constantly taught to elongate answers? Those who are succinct can’t meet the 5-page requirement, while those who use fillers and bs can. So what’s going on here?

And while we’re on the subject, why are there absolutely zero articles on the internet, news, opinion, comedy or otherwise, that are brief instead of a stinking short story?