Modern cars have crap suspensions/steering geometry for unassisted steering. This is a side effect of the geometry that helps keep their wide tires from making them wander all over the road. That said, it's only a marginal increase in effort. Modern cars are just fat. An Altima curbs at about the same weight as a base spec 2wd pickup that would have come with manual steering in the 80s and the Altima has a much higher steering ratio.