I know you've asked for something less obvious, but honestly it is very simple.
Either I got bored, or I shouldn't have subscribed in the first place, because it was not quite my thing... But sometimes I am like... well, maybe? Particularly if someone has not too many subs, I'd sub.
Also, well, for sequels, well, if I was excited to see someone get happy and what I see is them heading for more unhappiness, endless unhappiness, I just can't do it. I guess, one book I can manage, but two books in a row of misery, nope.
I was following a book where I loved one of the couple, hated their LI. The rejected guy I staned got a sequel, but his new LI I hated. So, at this point, I just dunno what to do. I can't love one of the two! I want to love both! I want to be loyal, but I feel i am going end up disliking the book.