Generally speaking, in order for a subscription model to make sense, someone has to be screwed. The subscriber has to get less value than they would by purchasing, the producer has to get less value than they would from sales, or the subscription service has to get less money than they would from sales.
There’s a small argument that people who subscribe to a service would watch or read things that they wouldn’t have bought, but that’s just redistributing income from high-value producers to low-value. Since I got a Netflix subscription I rarely buy movies any more, so the companies have lost all those $10-20 sales in favour of the few cents Netflix give them.
And it’s ten times worse with an uncurated service like KU, because it literally becomes a license for scammers to print money. KU is now basically the Hunger Games, where writers are thrown into a pit of money to fight to see who comes out alive.
KU eliminates the pricing mechanism that makes economics work, and gives scammers a license to print money. A bot costs $9.99 a month, and earns $0.004 every time it ‘reads’ a page. So it can trivially generate far more income than it costs.
Giving scammers the ability to print money is not something that can be fixed. KU is broken by design, as anyone could have told Amazon before they created it.
You can’t do the same by having bots buy your books, because Amazon takes a 30% cut. It’s only the subscription model that makes scamming profitable.
Of course, Amazon claim to be able to count page reads, but they really can’t, and it’s a fundamentally complex problem to solve. Unless, maybe, they restrict KU books to tamper-proof Kindles and put a face-tracking camera on the front to check you’re actually reading the words.
Hence scammers exploit that to make more $$$$$.