As long as the Boomer generation survives, there will be a hearty market for paper books.  I have a couple of books on Amazon and make some money on them. Many people prefer reading paper over digital, I myself am one.  I used to subscribe to several print magazines.  Once they went all-digital, I stopped reading them.  It is not only reading digital text that bothers me.  Navigation on a digital device cannot beat picking up a real book and flipping through the pages. Some things are just better in real print. 

Real books will NEVER go out of style because of the simple fact that they do not require batteries, and you cannot just click a button and delete a book from the internet because you disagree with what it says, otherwise known as, "Cancel Culture" that is running amuck all over the web.  There has never in the history of books been a law made banning a paper book that was 100% successful.  That may not prove to be true with things on the internet.  Everything online can be tracked digitally and as the world becomes more unified digitally and establishes universally enforced international standards based on the personal ethics of a few elitist (already happening), they day may come in the future where they may decide that this or that book should not exist, and simply delete it from the web (or at least for all common folk).

Despite all the unfounded, opinion-based, protestations to the contrary, what I said about the used book market is 100% factual.  People are making a lot more money off of selling used books these days than they did 20 years ago.  I said it before, and I will say it again.  "If you don't value your product, nobody else will either."   Regardless of how oversaturated the market is with stock photos, there is a base value for them.  That value may not be hundreds of fo dollars each, but it is not zero either.  That value is whatever it is to make it worth people's time and effort to create the content.  If all the people who right now are not valuing their work, were to pull their content down, overnight, prices for content would shoot up.

As long as the slaves are willing to work for free, what incentive do these companies have to pay more?

As long as the Boomer generation survives, there will be a hearty market for paper books.  I have a couple of books on Amazon and make some money on them. Many people prefer reading paper over digital, I myself am one.  I used to subscribe to several print magazines.  Once they went all-digital, I stopped reading them.  It is not only reading digital text that bothers me.  Navigation on a digital device cannot beat picking up a real book and flipping through the pages. Some things are just better in real print.  ....

wrong again -in fact, preferences for print/ebooks are similar across all generations

i read 50/100 books a year (60-70% kindle) plus 10+ print magazines/mo

navigation is easier on kindle - where else can you search an entire book for a name or phrase in seconds? or maintain dozens of notes, comments and bookmarks that are easily retrievable?  in our book club the kindle users are the ones to solve most questions!

kindle is usually cheaper, only regret is i can't give the book to a friend. ebook footnotes are much easier to use (DFW fans take notice!) and there's NO comparison to reading a 800+ page small print paperbook on a kindle!  my arthritic hands much prefer the kindle.

https://www.independentpublisher.com/article.php?page=2456

https://experteditor.com.au/blog/infographic-surprising-reading-habits-millennials/

https://www.libraryjournal.com/?detailStory=Reading-Through-the-Ages-Generational-Reading-Survey

Despite all the unfounded, opinion-based, protestations to the contrary, what I said about the used book market is 100% factual. ....

how can it be factual when you offer no actual evidence? and, anyone who disagrees with your (unsupported) claims is wrong?  one person showing the opposite of your claim makes the 100% statement untrue! maybe you're talking about selling your own books on amazon - but that's a miniscule part of the book market -- i've sold books on ebay / amazon since around 2000 and the market for MOST books has fallen thru the floor, as large booksellers can sell from the basement.  it's difficult to find any book that will bring you more than $5-10 gross and with amazon fees, shipping ($3-4 ), inventory management, anyone w/o low wage workers can't compete.  (my ebay/amazon monthly sales are 1-2 times what images bring in, but i've found my niche and have an inventory of over 1000 items and only a few dozen actual books still online)

The value of anything is what someone is prepared to pay for it. If someone can't make a profit from that then indeed if its their living they should do something else. It is true that if huge numbers of people stopped submitting to free or microstock sites and withdrew images then the value would increase. There is simply no evidence that this is happening.  Just as with books the market for images has many segments which will fare differently. I can get a copy of Nicholas Nickleby for �1.50. A first edition is several hundred pounds. Microstock is a market for low production cost or mass appeal simple images for emphemeral marketing/blog purposes. If you are producing expensive ultra high quality images that are in demand then selling them on Mstock is the equivalent of selling first edition books in a car boot sale.