On a percentage basis? Isn't that because they're the most common?
Probably not due to commonality but as they weren't the recommendation of the agent.
The agent, like the owner, doesn't know the applicant (unless they have previously rented through them/previous relationship) but that is not to say that what looks good on paper/reference checked etc can't go pear shaped.
Are you going to make the agent shoulder the blame for leasing commercial space to a publicly listed company backed by James Murdoch & Jamie Packer which then went belly up?