I never understood hate watching. Why bother watching something you call boring and trash every week? Either you are lying and you are entertained or you are crazy.
Or you've a more academic curiosity of where the show's missteps are.
I have trouble understanding it too. Narag makes a good point, there is some academic value in trying to ascertain where the show missteps, but at the same time I only feel like a few people are actually doing that and most hate watch something out of sheer disbelief that whatever they aren't enjoying is somehow popular. I don't think I've never watched something to the end if I knew I loathed it before the mid point.
I rarely, if ever, see people doing the same with a show that has failed to find a large, vocal audience. I mean, look at just earlier this year: Hand Shakers. After the first episode disappointed so many
No one was watching save DTL. The only time anyone trashed it was when DTL sung it too much praise or recommended it. No one could be bothered to care about it because it wasn't popular.
That said, also plenty of fans actively review anime, either for their websites, blogs, our out of sheer fun (I guess this kinda counts as academic.) I imagine a few people could simply be sticking with it because they decided they'd do a write up for it at some point.
If I just want to see how it ends. Aldnoah Zero, Charlotte, and Guilty Crown are good examples of this for me. I went in with anticipation, got disappointed around halfway through, eventually hated it before the finale, but I was so far in, I just wanted to finish it.
Sometimes, it's just not worth it though.
This I can totally understand though. I was iffy on Cross Ange for example after Episode 1, but the show gradually won me over till pretty close to the end. It wasn't ever an amazing series, but there was an appeal to it. As we reached the final episodes the show, as most know, gets incredibly bad, but I was so invested in it by this point I felt I had to finish, even if it was actively turning me off at this point.