Why write a series? With Sara Rosett
"Readers love a series. If you can get your readers hooked in on book one, then book two and three on down the road is an easier sell perhaps than a standalone because your readers are familiar with the characters in the world. If they enjoy the experience, they want to return to that same world again.
And then there's some financial stability with writing a series.
If you know that book one made a certain amount of money, then maybe book two and three may not be that exact amount, but you can predict a little bit.
And not always, but sometimes, writing a familiar series and characters can be a little bit easier and it can go faster because you already know the world. So you're not world-building with each book.
And then, there's marketing reasons for promotion that make a series a good thing to have. You can save time, you can focus on book one in your marketing, and then you're not trying to run ads to all the books in your catalog, you can focus on one and hopefully as readers come into that book one, if they like it, they'll continue on."
Full interview on The Creative Penn Podcast