In fact, there is. George R.R. Martin has very specifically answered this question.
In this interview with Charlie Jane Anders, GRRM says:
I get complaints sometimes that nothing happens(in AFFC) — but they're
defining "nothing," I think, differently than I am. I don't think it
all has to battles and sword fights and assassinations. Character
development and [people] changing is good, and there are some tough
things in there that I think a lot of writers skip over. I'm glad I
didn't skip over these things.
Coming the point of this question, he says:
And that has been interesting, you know. Jon Snow as Lord Commander.
Dany as Queen, struggling with rule. So many books don't do that.
There is a sense when you're writing something in high fantasy, you're
in a dialogue with all the other high fantasy writers that have
written. And there is always this presumption that if you are a good
man, you will be a good king. [Like] Tolkien — in Return of the King,
Aragorn comes back and becomes king, and then [we read that] "he ruled
wisely for three hundred years." Okay, fine. It is easy to write that
sentence, “He ruled wisely”.
What does that mean, he ruled wisely? What were his tax policies? What
did he do when two lords were making war on each other? Or barbarians
were coming in from the North? What was his immigration policy? What
about equal rights for Orcs? I mean did he just pursue a genocidal
policy, "Let’s kill all these fucking Orcs who are still left over"?
Or did he try to redeem them? You never actually see the nitty-gritty
I guess there is an element of fantasy readers that don't want to see
that. I find that fascinating. Seeing someone like Dany actually
trying to deal with the vestments of being a queen and getting
factions and guilds and [managing the] economy. They burnt all the
fields [in Meereen]. They've got nothing to import any more. They're
not getting any money. I find this stuff interesting.
And in this Rolling Stones interview, he sums it up with:
In real life, real-life kings had real-life problems to deal with.
Just being a good guy was not the answer. You had to make hard, hard
decisions. Sometimes what seemed to be a good decision turned around
and bit you in the ass; it was the law of unintended consequences.
I've tried to get at some of these in my books. My people who are
trying to rule don't have an easy time of it. Just having good
intentions doesn't make you a wise king.
TL;DR; A good human being doesn't translate into a good king. Dany is good, just, ambitious, wants to end slavery & give freedom to the oppressed. She does that, but what happens after that? What happens to the oppressed and enslaved after they gain freedom? How does she rule a kingdom when she wins it?
If all GRRM wanted to write was an epic war novel, he would have written about the Mad King's reign, & how Ned & Robert thwarted his unjust rule.