One man's "gate-keeping" was everyone else's curating. The old model printing and distribution was a very real cost, usually two large to be borne by an author and certainly by a new author. The primary sales channels also had a premium on space, you can only put some many books on shelves low enough for customers to browse, their are only so many end aisles privilege products with placement showing more than their spine, and the story with magazine racks wasn't much different.
So the publishes provided enormous value to retail by both ensuring quality control, and filtering for what the public wanted to buy or was worth convicing the public they wanted to by thru various literary reviews, direct advertising, etc.
Digital has removed the *need* (and many of the retailers with that).
The question is was and remains how much value was the curating, QA to the consumer. We were reading/listening to better content because of the filter and not wasting on time on drek, alternatively what price were we paying for the gate-keeping aspect in terms of not hearing voices and ideas that might have proven interesting. What is the cost of the fan out. When everyone was pulling from the selection on the shelf at the local Books-A-Million, Dalton, or library shelf, there was good chance of running into someone who'd read the same thing you did. Now - FAT chance if someone actually read something it was probably a substack, or some Kindle E-book by someone you never heard of.. As with water-cooler television even if what we are consuming is very good the opportunity to have any local discourse about or discourse within your own social circles whatever form they take is nil because you must first convince someone else to make the investment in it.
It certainly is having an effect on social discourse and how ideas advance and change in our society and I think very likely calcify because their is no collective train of thought. As to the topic at and AI is just going to pour gasoline on all of this, it will absolutely eat the proofing, editing, polishing value the traditional publisher can still add in the ebook era. The incentive for various retail channels to 'stock' the stuff of least providence will be huge, if an algorithm can see sell Christine Middle Schooler another book about sparkling vampires and her Dad another story about manning a first generation aircraft carrier in the Pacific, she likes those and so does he, and they can pick from ones with almost no royalty/residual attached, more profit for them. If AI can make those good enough to get them to come back for more; what need for a traditional publishing house is there, that would pay the bills anyway?