Hi @systaran (and @whyvon and @Collie1313). I agree; it doesn’t really say why, does it?
From a business model, maybe it’s harder to attract/keep PPs (pet parents)? It reminds me of other sites and how users may feel there’s a lean by the company one way or the other: Airbnb hosts vs guests, or eBay sellers vs buyers. Each side probably wishes things were a little different.
These forums are mostly sitters, so we mostly hear just the sitter side.
What I wish is that PPs at least had the option of a free background check like sitters. Similarly, I wish PPs could get external references to start out.
I think it would actually help the PPs. It’s hard to start out as a PP, especially if you’re not in a popular area. As a sitter, I may think, “Do I really want to be the one to test the waters? What if they ask me to build a doghouse?” That was based on an anecdote from elsewhere. 
Anyway, I don’t care if your references are your friends/family. At least you’ve got friends and family who will vouch for you in writing.