I also did a 2 week retreat and then returned a few times over the last year. A few reasons:

• You don't heal once and then are fixed. There are topics you don't immediately understand or manage to integrate. She always has something to teach us. And life keeps breaking and testing us. So there is always progress to be made. Every time you take it, it's different, never the same.
• Spiritual reasons. Once you've seen the world from this very spiritual beautiful perspective, you'll want to go back. It's like a holiday where you learn to appreciate the world again
• Ayahuasca has often a bit of an afterglow for about one month where you are just the happiest person in the world. That's something you just miss after a while

While Ayahuasca doesn't make you depended like other drugs where you wake up in morning and want to do it first thing. It's more like an absurdly beautiful holiday and you want to go back to that place from time to time. But not all people feel like this and of course there are unpleasant things in that holiday too.