To be quite frank, it's because some threads have reached such gargantuan proportions that they dwarf the likes of Jupiter; then also have to wade through the inevitable plethora of total gobshitey comments from folks who are Meany McMEANERSON etc. Without fail you'll get on most large threads:
OMG YOU ARE SO UNREASONABLE YOUR POOR CHILD/PARTNER/PARENT/variation thereof
multiple consecutive posts from one person to correct typos or add things they forgot (guilty as charged)
Or it will be a pile on from a sewing circle whereupon you are labelled SATAN in some form or another..
Endless flowers and hugs (which are lovely I ain't knocking it)
Someone playing devil's advocate.
People getting bent out of shape at those playing devil's advocate.
"This will end up on the daily mail.."
A bajillion well meaning and genuinely lovely folks asking after the OPs well being/update etc
Folks comparing it with similar threads and trollhunting
Some really EPIC SWEARING (some of the best bits)
Comments such as "are you havin a laugh/takin the piss/etc"
Tons of LTB and dump him..
The usual suspects saying "THAT'S A HORRIBLE THING TO SAY - REPORTED."
And that's not even all of it. It's all great and entertaining, but bloody hell it's hard work on yer eyeballs when there's so much of it...
..and that is why I do not always read the whole fucking thread. Most of the time I do - but if it's massive - nope. I look for OP updates and salient points.