Because it isn't simple.
Sorry, science can't crush volumes and volumes worth of information into one single, easy-to-understand sentence like a pastor can (pretend to do). Either way, I'd say the overall benefits of its existence in the last 250 so years would heavily outway an outdated book by goatherders.
Goatherders from thousands of years ago: This is the infallable word of god.
Reaction: Oh, obviously.
Scientists, modern people, from all ages: This is an obversation that I made, and I am simply noting the obversation that I made. In order to ensure my own personal observations are worth a ****, I will do something called an 'experiment' which allows to empirically measure the observation of such phenomenon, in which it can be tested and created thousands and thousands of times by anyone who wished to do so.
Reaction: Where's the evidence that what you are saying is right?!
Scientists, modern people, from all ages: Because I ran the experiment. If you run the experiment under the same conditions, you will get similar results.
Reaction: See, I know you couldn't explain it. I'm going back to the goatherding book.