[djur]

I think that's the point -- "very sad" is unpoetical because it doesn't convey anything more than "sad", which is itself a generic word. If you're writing poetry or fiction you want to be describing emotional states more interesting than "sad".

The important corollary here is that not all language needs to be poetical. It's OK to use generic language in a lot of situations. Sometimes "I'm very sorry to hear that ____" is the tool for the social situation.

[derbOac]

"Very sad" is simple and to the point. There's many situations where anything else would sound inauthentic.

[saurik]

I mean, the goal wasn't to sound "authentic", it was to avoid sounding "lazy" while trying to "woo women", which is the only situation considered relevant in the supposedly-inspiring speech by the maybe-a-bit-creepy professor.