Very misleading. You've lumped all decades of U.S. slavery as if conditions for escape remained static since 1776, and you've omitted the necessary explanation that you can refer only to those fugitives that were caught (a requirement of being returned), not all fugitive slaves.
It's more relevant to the period most of us are interested in here to point out that by 1800, even in the free states, fugitive slaves were as likely to be successful as they were to be returned. This exact circumstance is was what drove the South to bulldog the Fugitive Slave Act. They considered it necessary to the survival of their system in a more mobile world. Horses and dogs could no longer get it done.
From the fugitive's standpoint, there were significantly-increased opportunities to escape via a vastly-expanded network of improved roads by 1800, with new canals and (steam) boat and train routes soon following. Also, there was a rising tide of anti-slavery sentiment and awareness in those areas of the Country they were escaping to, especially after 1850, as we know.
