DK,
I've had similar experiences. For one publisher I would have loved, my manuscript made it past the acquisition editors, but was rejected by the marketing team.
Another said I needed to show more and tell less, and another told me about being too encyclopedic.
So I keep rewriting, trying again, have other WIPs.
But also, I have self-published a book of fairy tales, and am working on a book written from our cabin journals, a family project I will self publish for Christmas presents and sales. My sister will design a cover, my daughter is helping put the ten years of journals in the computer, and my husband is taking photos around the place. Over fifty family, friends, and friends of family and friends come to this cabin each year and some will purchase copies.
I always need some project, whether it will ever be published or not. And it is all practice.
Carol