I've known a number of folks who have done "read more" challenges, whether 50 books a year was the target or some other number, and while this is surely anecdotal, the real goal wasn't hitting some arbitrary number, but simply to encourage reading more, and prioritizing reading as a hobby.

As someone whose greatest pleasure is a day off with a good book, it's hard to balance reading with all the grownup responsibilities we have, and as a leisure item, it's usually the first thing cut from a busy day's schedule. Reading a book a week isn't as much about the number, but by gamifying the outcome, you prioritize it above things you might otherwise not.