Why don't books get translated?
If you think it's because it's hard to find willing translators, or because the skills required are too rare, I'd like to offer two case studies below that point to another explanation:
The reason translations don't happen is that we prohibit them. That is to say, translations are what happens naturally, except when copyright restrictions suppress them.
If you're skeptical, consider the following tale of two authors, one whose books are free to be translated by anyone, another whose books are not.
We'll even stack the deck a bit. The author whose books are freely translatable will be a relatively minor author, one whose books are not, to be perfectly honest, of earth-shaking importance. Whereas some of the the books by the other author are acknowledged masterpieces in their original language, and you will see quotes from a prominent scholar about how the absence of translations is "one of the great intellectual scandals of our time".