Perhaps hitchhikers are realizing that they have a much better chance talking to someone at a gas station or truck stop first hand so that they actually get a ride otherwise people are probably less inclined and more reluctant to pick up strangers lately. The first hand real contact so that people can make a judgment is a better way to go than the few seconds it takes to make a decision while getting on an on-ramp.
Whatever the case it seems to be a trend, which may not easily be reversed in the future. Maybe this is a good thing? Was it all the movies and scary horror flicks? Is it the new attitude of police harassing them and writing up little slips with proof of identification? Where did they all go anyway? Think on this?