There are even threads that have more than thousands of replies and if you will scan through it most are redundant and generic replies. However, it seems that there's nothing to be done because there are even other threads that are almost the same as other thread but just rephrased.
This was mainly due to spammers that wanted to rank up fast or rank their alts fast. Hopefully the merit system would solve one part of this issue.
The next part of the issue if that people generally don't lock their thread after their question is answered or they got enough replies to form an opinion. I assume some of them aren't aware of the "LOCK" button on the bottom of the screen.
Another thing is that everybody feels an urge to comment on things (I think this is human nature) even if their contribution isn't really going to change something or add something to the discussion, they just need to feel heard.
Maybe a solution would be to automatically lock threads (e.g. after page X fills up) but still leave an option to the OP to re-open if needed.