This limitation makes sense.
Don’t post no-content replies.
Quoted from the FAQ
Here’s a thought about the rationale behind this:
When in a discussion with others we verbally signal our active participation , agreement or disagreement (like “exactly”, “yes”, “agreed”, “mm-mm” or “nu-uh”, “no”). These are short interjections sometimes accompanied by gestures (nodding, hands) and temporal. After a discussion or dialogue about certain topics , noone would recall the exact reaction (unless very expressive) but rather the disposition expressed (‘I am listening’, ‘I agree’, ‘I disagree’).
In written discourse this wouldn’t work. any interjection (short answer) would clutter the log and make it difficult to follow the actual topic. Think of it like everyone saying their thoughts on a matter at the same time. Understanding every party’s position becomes very difficult.
The audience of a topic on this forum is potentially much higher than that in a every-day dialogue happening face-to-face . Hence the limitation on short answers.
So while may feel wrong for our natural impulse it is justified to require “substantial” answers above the reaction / interjection level.