Maybe authors are just tired of waiting? Publishing houses haven't gotten worse, but they work by their own logic: you need an agent, then a long manuscript review, then negotiations, then you're in the queue for release. All of this takes years. And in the meantime, the author can just upload their book to Litres in a couple of weeks and start earning right now. Plus you have full control: you pick the cover, release date, price, and formats yourself.
I know someone who told me a story about her friend who wrote romance. She spent two years trying to get into a publishing house, rejection after rejection. Then she gave up, self-published through one of the platforms - and suddenly her books started selling well. Now she releases several books a year on her own and makes more money than she ever dreamed of through traditional publishing. Turns out her audience was looking for her on the internet, not in bookstores.
The thing is, for a large part of authors, self-publishing isn't a consequence of a publishing crisis - it's just a more convenient option. You need a publishing house if you want to be in stores, on shelves, in literary award shortlists. But if your main audience is on social media and reads through apps - why wait for a publisher?