The Indie Book Stigma

As an author, I am always keeping my eyes open for opportunities to promote myself and my books; it’s one of the things you have to do as a self-published author. No one else is going to do it for you.
And whilst I’ve found many amazing blogs and sites that have helped me (and to whom I am eternally grateful), I’ve found many that start off their review policy with “I will not review self-published or indie books.”
The question I want to ask is, why not? Please note this isn’t an attack on reviewers or bloggers, it’s your site and you can do as you please. I am just honestly curious. I want to know the reason behind it.
If you are a blogger/reviewer who happens across this post (as I assume most of my followers read/write indie books already), please let me know. If you don’t want to post in the comments, please feel free to email me at aprillelegacy(at)gmail(dot)com.
I will not attack or judge you, and I hope you will award me the same courtesy. I would really just like to know what this stigma is.
If you’re an indie author who has come across this as well, I’d like to hear from you. Same deal, comments or email me :)