Many published authors are actually hybrid; working with both traditional and self-publishing industry, and most of them started from being an indie author. So, why self-publish first?
Traditional publishing is not so easy to get into. Your manuscript has to undergo different stages of reviews. Being approved by the initial review doesn’t give a guarantee that it will pass the next through the final publisher’s review. And most often, you get a lot of rejections.
Self-publishing your book gives you an instant chance to get published as soon and as is the way you want for your book. Hybrid authors use this opportunity to entice potential traditional publishers.