The barrier to publishing a book is more or less non-existent. The barrier to getting a publisher’s name that is sufficient for someone to think (rightly or wrongly) that this book has a legit stamp of approval is somewhat higher if not all that high. And obviously implies that those publishers have to gatekeep to some degree.
Sure, we turn away crap, but so what? We don’t have a cap on how many books we can publish other than the time, labor, and money resources we have. Which are finite. We could publish more than we do now, and we have in the past.