Because this a very naive (intended or not) view of the book publishing industry. Yes! everybody can write a book, at least in theory, but that is just 5% of the task. How about distribution, editing, advertising, shelf space in the bookstores, reviews, etc. A book who cannot reach potential readers may as well not exist.

And somehow only the bad writers get through with that, because everybody conspires against the good writers? Give me a break.

It's also not even true anymore. Most of the things you listed you can get for free or almost nothing these days.

In threads like this, you should then also be able to point out the really good books that failed because they couldn't find a publisher? Where are they?