First off, what's the "learning curve"? I've nicked this phrase from Brandon Sanderson, so I'll tell you what it is to him. It's your readers learning about your world. It is highly prevalent in speculative genres for pretty obvious reasons. We're entering a new world.
The learning curve can equally refer to the process of your reader really knowing what's going on in the plot. That's a highly related issue, so I'll touch on it.
I was watching one of Brandon Sanderson's many awesome lectures on Write About Dragons, when he asked the class why we should write with short, sharp description. Credit to the class: they touched on it. All the same, I wanted to scream through the computer screen at them, which I why I'm screaming at them through a blog post now.
We do it because the reader wants the story. Simple as that. They want to know what the smeg is going on. "Matt jumped over the wall." That tells us what Matt's doing. We' know there's a wall there, we know he's jumped over it, and we know, by strong implication, next time we see him he'll be on the other side of it. Great. The rest is shading.
Shading is great. So long as you don't consistently resort to adverbs and adjectives. "Matt swiftly bounded over the abundantly tall wall of stone that was built in 1946 when German settlers came to Townsville on boats made of oak trees, which were a common tree in Germany back then, hence being used to create the many boats that the settlers, one of whom was Matt's great great great great grandfather, used in coming over the Atlantic ocean, which is the world's second largest ocean and" AAAAAAAAAAAAAAAAHHHHHHHHHCKKKKKKKKK!!
That's the ultimate way of doing it badly. We've got pointless adjectives, we've got useless information, we've got more useless information that stacked upon the first stuff.
So what do I mean by shading, and how can one do it well? The biggest problem above is that I told you all about the wall. It didn't have anything to do with the story. "Matt shifted his weight to the crutch, swung his bad leg onto the wall's edge, and cried out as the bullet wound stung afresh." That's not amazing. It's off the top of my head. But you get the point. The fact that Matt's using crutches, and that he's got a duff leg because he's just been shot, has to do with the story. I shaded his act of jumping in ways the reader might find interesting.
So again, what's the point? The reader wants to follow your character through your story. They don't want you leading them off somewhere pointless.
How's that relate to the learning curve?
That's the other thing Brandon Sanderson was talking about, and he mentioned how people so often in Mid-grade fiction begin in our own world. Why is that? Why does that solve the problem of the learning curve? (The problem being that, given that the reader must understand a new place with new rules, it's very easy to muddle the story. It's also a wonderful thing. It just raises certain issues that must be addressed.) The class touched on it, again to their credit, pointing to the way you get to enter it gently and so forth. They missed the point, though, which ties to how we want to follow the character through the story.
In those books, the learning curve is an inherently vital element of the character's journey through the story. Frequently (Peter Pan, Narnia, Alice Through the Looking Glass and many others) the learning curve, an a legitimate sense, IS the story. We have instant fascination with the things we're going to learn for the exact same reason that readers don't want meandering description: readers want to follow a character through a story. That's why we read.