Ok, this may come across as b*tchy, but I've been called worse

Those of you who go into a thread, skim it and then say "I haven't read all the replies, but" - why? 90% of the time when I've seen someone do this, whatever they've said has been said at least once before. Why not read the thread? Why admit that you couldn't care less about what other people have to say and just want to have your say?
I'm not trying to be nasty, I just don't get it

And I promise I will read every single reply this thread gets