Pure and simple.
All publishing deals are not created equal. A contract in hand from a reputable publisher who will do a fine job on a book, and keep it in print for years may still not be lucrative enough to be a good risk for an agent.
It takes just as much time and energy (actually MORE) to do a $5000 deal as it does a $50,000 deal.
And most agents want more $500,000 deals, not more $5000 deals.
If you find yourself in this position there are two things to know:
1. You don't have to have an agent to be successfully published.
2. You MUST have someone who knows publishing contracts review your offer and advise you on what changes need to be made. If you need the name of a contract review specialist, email me and I'll give you one.
I've had to say no to some really wonderful projects simply because there wasn't enough money in them. That stinks, but reality is often odiferous in the extreme.