Angry Grimace
Two cannibals are eating a clown. One turns to the other and says "does something taste funny to you?"
I get where you are coming from but people never really engage anymore so it's hard to post much more than a short impression to see if people have a more focused opinion.I started thinking the same some months ago. But I've been silent until now.
It's because MangaGAF sucks. I would say I like more manga than anime, but animeGaf is better than mangaGaf.
90% of the posts as you said are one-liners, super short impressions of a new chapter. They are so short that are worthless, they basically are "this is good", "this is lewd", "this is so-so", "X happened", etc.
In truth, I consider that what's truly happening is people saying "I'm reading this" in a roundabout way, that's the true meaning of their posts. At least that's the only meaning I get from them. It's like annotating in MAL what they wrote.
People will put excuses like "well, this manga is weekly so usually there isn't a lot to say from just 20 pages". It isn't like after watching a 60 minute episode of a HBO series, you see.
Well, if nothing happened worth commenting, maybe they shouldn't post a fucking comment. It isn't that hard. You don't have an obligation to write in the thread every time you read a chapter of something, maybe they should do it when they really have something to say that it's worth sharing in a specific chapter. Or maybe write a post every 6-7 chapters commenting on how the series is going. Or if it's a short manga don't write the moment you read 2 chapters, wait until it's finished before writing the impressions.
If we were in a Offtopic or even gaming side, some mods would give bans for the high amount of spam messages with low content, you aren't supposed to write a 5-word comment of a game for every 10 minutes of play you do or even 5 minutes of a film you are watching, but this is Community where things are more left unchecked, threads are allowed to be more a stream-of-consciousness / informal chat.
A few examples from some pages ago
The funny thing is that the half dozen people that mostly post in this machinegun style and also read the same series don't bother to discuss or engage each other comments. Each one just drops their 6 words sentence and usually that's it.
It's easier to do on somewhere like Reddit or Something Awful where individual series get their own thread but I really like GAF so I'm gonna just post a short impression if I have one. If people don't react they don't.