I can’t speak for her, but there are good reasons to keep playing in your sandbox instead of new ones.

For one thing, a writer can’t just magically turn things on and off. You’re kinda stuck with an idea until it runs its course inside you. Doesn’t matter what anyone else thinks, some stories just don’t quit when you finish an arc. Some characters won’t go to sleep, they keep scratching inside your mind to get out and live more.

Then, world building. You put a lot of time and effort into setting up something like a dystopian future, then tear it down in your trilogy. But all that other stuff is still there. Why waste it? Why not share that too?

Added to that, some worlds can hold multiple stories. And, if that world you built is deep enough and broad enough, stories are going to pop up there, even if you didn’t intend them to. Like, what’s happening on the other side of the world from where the hunger games trilogy was set? Maybe you didn’t think about that when you’re writing the first series, but now you’re fielding questions from fans, or even just thinking as you deal with some old notes or whatever, and now there’s this story in your head that belongs there.

Are you supposed to force yourself to build a different world just because someone is going to complain about it being “milking”? Fuck no. You write that shit the way you want to, and you’re set up from success already, you don’t have to pander to haters, you only have to please yourself, and your publisher. As long as the stuff sells at all, you’ll likely have plenty of people that enjoy it, so fuck the haters.

Sometimes, you’re bored and don’t have any better ideas, so playing around in your old sandbox is as good or better than anything else.

And, yeah, sometimes you wanna pad the bank account because George believe it or not, even movie money runs out, and writers are like any artist, you don’t have a company covering part of your insurance, or whatever. You work for yourself, which means your have to deal with all the taxes, all the little bills, all the expenses all on your own, which can eat into your savings/assets faster than royalties come in. So you kinda gotta pick your chances of more success.

You ever see how many writers have multiple series with no connection that the other series sell just as well as the most popular one? It ain’t many.

Plus, it’s damn near the same as as writing in only one genre. If someone is writing only horror, as an example, that’s no better or worse than expanding one setting. It’s barely different, especially when the author ends up having connections or a shared universe down the road.

You write for a living, or try to, and the number one rule is “write, dumbass”