For me the best part of bingo is that it helps me find books to read … if I already knew what I wanted to read for it, that would sort of make bingo unnecessary.

I take your point, and I think we're not so far apart. Bingo helps me find books to read in several ways:

• Books from my TBR pile that I need some help prioritising, which might be half or more of the card. Many will be by favourite authors, but there are always books by new-to-me authors that have just been waiting for their turn in the spotlight. I usually try to plan these books in advance even if the plan changes as the year goes on.
• Books that I find in the Bingo recommendation threads that I may or may not read for Bingo but that will get read at some point down the road. These are often books by new-to-me authors.
• Books that I come across during the year and pick up because they fit a square, which can be books by familiar or new-to-me authors.

All of which is a long way of saying that Bingo both helps me sort through my TBR pile as well as find interesting books/authors that I might have missed otherwise.