Or Richards was afraid that the government people would find out why he was running, in which case he'd only be trading one set of problems for another.
That's the logical answer. Considering the nature of agencies such as the FBI (and any other you can name) in the early 1970s, who in their right mind would trust them with a secret as amazing / important as immortality? Ben Richards would have placed a noose around his neck.
While The Immortal
TV series borrowed The Fugitive
template, the original TV movie was a very different animal, using pathos to rip away the assumed thrill of learning that Richards will live forever, with the chase element only occuring in the last act of the film.
The TV movie was not a page-for-page adaptation of the James Gunn novel which inspired it, but the changes worked for the format.
Unlike characters before (Richard Kimble) and after (David Banner), pilot movie Richards also has a relationship he elects to end because of his situation, adding self-inflicted pressure his TV counterparts did not experience; in the pilot of The Incredible Hulk
, Banner's colleague/love interest died in the pilot, while we know what happened to Kimble's wife.