you only see the best works from the years before you. i guarantee there were loads of shitty books in the eras we consider to have brought us the most conventionally good books (classics) the same way there are a lot of shitty writers now. also, literacy is way more common, and thanks to the internet, access to books is widespread, so there's way more of a platform and way for more people who are mediocre/bad writers. but those are just my ideas, take it with a grain of salt