How to ask guest author to write for you?

So, I get a lot of guest posts request on my website and some of the guest authors have written some amazing content. After they publish the article, I usually ask them if they're interested in writing more for our website but most don't agree.

I wanted to know how can I ask these guest authors to write more article for the website. Or is that even possible considering most of them want to just publish 1 post.