Why are people uploading so much AI junk?

Poor quality images were likely grandfathered in from the past when acceptance criteria was less discerning.

"First and foremost, the images derives from the hard work of photographers."

There is the reason Adobe has decided to get into the AI business. Once out of beta, Firefly will use Adobe's own stock database, plus images in the public domain, to generate AI. I'm sure I'm over simplifying this, but it is Adobe's intention, as I understand it, to complensate stock contributors if and when their images are used to create other images. I also suspect that there will be a means by which contributors can opt in or out of having their images used for the purpose of generating AI. Until any or all of that happens, Firefly and Generative Fill in Photoshop will remain in beta.

As the issue of approprating the work of others plays out in our court system over the use of copyrighted material used to create AI, I believe this will eventually become the standard practice--and possibly the requirement--of all companies now in the business of letting users generate AI content. It may take years before this happens, but Adobe is clearly going to be the front runner with respect to a more fair system of the practice.

"The next thing is that in the near future anyone and everyone will be able to create images and the agencies will be swimming in images"

That's not in the near future. That is true now. Anyone and everyone can create their own AI images. But will they? Anyone and everyone can now build their own web sites with the variety of relatively low cost (and sometimes free) web site building applications now online. These sites may have put a few web site designers out of business, but certainly not all of them. I'm freelancing for a company now that wants me to edit their products by knocking out the backgrounds of their product images for use on their web site. The images were taken by a professional photographer, so no job was lost there. They are pretty much handling the web site themselves on their end, but they don't have the time or the know-how to turn their product images into transparent png's. In fact, they recently sent me a QR code png that they wanted me to turn into a reverse image, from a black QR code on a transparent background to a white QR code on a transparent background. This process can be managed with one click in Photoshop. But the individual who hired me wanted me to do it for him, even though the company leases the entire Create Cloud Suite. I literally even told him, "No charge for that one." His response? "Charge me for everything."

Stock agencies aren't going to go away. There will always be people and companies willing to pay for people with the skills and talent to do things like this for them. These people are managers and CEO's. They don't want to be bothered with learninng how to generate AI themselves, or to build web sites, or to use their iPhones to photograph new products.

Will there be a lesser need for photographers in the near future? Of course. But the vast majority of them are not going to be put out of business. Nor are models. As I beleive I may have stated elsewhere, it will still be a long time coming before we see an AI version of a Sports Illustrated swimsuit edition.

Meanwhile, progress marches on. Whale order producers went out of business with the invention of the electric lightbulb. Milk deliverers went out of business with the invention of the refrigerator. There will be fewer need for Pizza deliverers (or Uber or Lyft drivers) due to the advent of delivery bots and self-driving cars, fewer need for cashiers due to self-checkout lanes, and fewer need for bank tellers due to ATMs, Polaroid filed for bankrupty and was eventually sold to Bank One's One Equity Partners, while Kodak is barely hanging on due to the advent of digital cameras. And yet, there are still companies like Fuji who continue making traditional films and printing papers for people who refused to jump on the digital camera train. And let's not even bother talking about the vinyl record industry after digital music came into play, or Blockbuster after after video streaming became the way to go.

Everything is going to change. And yet, in some ways, nothing is going to change. We'll just have to wait and see.