I don't read to become an expert on something. I read to expand my knowledge.
I see books as windows. But there's a difference between seeing an ocean through a window and swimming in it. If you read a book on birdwatching, you now know more about birdwatching than the general population, but you're not an expert birder. Nor are you even a birdwatcher, per se.
Becoming an expert is more than reading books. Becoming an expert is experiential. That's why I like to write about things I've had genuine experience in, not just things I've read books about.
That being said, I can't possibly experience all the things you can in the world. Hence I read books. It's a safe way to get out of my comfort zone and explore the world without diving straight into the deep end.