Why not use any of the great KV stores out there? Or a traditional database even.
People use object storage for the low cost, not because it is a convenient abstraction. I suspect some people use the faster expensive S3 simply as a stopgap. Because they started with object storage, the requirements changed, it is no longer the right tool for the job but it is a hassle to switch, and AWS is taking advantage of their situation. I suppose that offering an alternative to those people for a non-extortionate price is a decent business model, but I am not sure how big that market is or how long it will last. And it's not really a question of better tech, I'm sure AWS could make it a lot cheaper if they wanted to.
But object storage at the price of a database with the performance of a database, is just a database, and I doubt that quickly reinventing that wheel yielded anything too competitive.