I have this problem as well, only gotten worst lately due to time restrains. I think the problem is tied to a fear of missing out on something good to read or play, with so many activities vying for our time and attention it's only natural that some things get left behind.
I have a huge backlog of games noted in vndb, it used to bother me a lot due to my completionist nature, but nowadays i accepted the fact that i can't take on so many things to play or read.
My advice? set an objective for a vn you want to finish, like completing the common route or a specific character route in a week, or