At 36, I can expect to live another 45 years or so, barring any surprises. Before getting a Kindle I was reading maybe a book a month (in recent years; I used to read more often). Now I’m reading a book every week or so. A book a week for the next 45 years is another 2,340 books before I croak.
On the one hand, 2,340 books sounds like a lot. But on the other hand, it makes it easy to calculate the “cost” of a given bad book in terms of lost opportunities to read good books: 0.043% per book. Every 25 bad books I finish represents roughly 1% of my estimated remaining lifetime reading opportunities. And the older I get, the more each bad book will cost.
In a rather long nutshell, this is why I usually don’t finish shitty books.