Why do people make rants on Meta Stack Exchange sites?
rant, n. 1. a. An extravagant, bombastic, or declamatory speech or utterance; (now esp.) a long, angry, or impassioned speech; a tirade. (OED)


Why do people make rants on Meta SE? translates to What makes people get emotionally upset in a social situation and then express their emotions?

I'm not going to go into this, because the answer is at the same time banal and overwhelmingly complex.

The only aspect that differs between social life online and away-from-keyboard is the higher level of anonymity online. Otherwise it is a common fallacy to think of the internet as being somehow not like "real life".