Whilst it is true that the existence of steep hills can reduce the likelihood of people cycling, the effect is gradual. For the most part, Bolton is not too hilly for the majority of people to cycle, especially if decent infrastructure means that they are able to ride on the main roads rather up and down the valleys.
Amsterdam may be relatively flat, but people there tend to ride heavy, single speed cycles, and their flat landscape means they often experience strong headwinds (sometimes called “Dutch hills”). With just a modest number of gears, most of Bolton is accessible by cycle. Even for people who still have a problem with hills, electrically assisted cycles make it feel flat and, at a fraction of the cost of a car, they are selling fast.
The lady on her e-cycle in this video left me standing without even breaking a sweat going up the hill at Walker Fold.
This 5 years old e-cargo cycle company gave short shrift to the naysayers of Bath.