I'm trying to figure out what makes a passenger traffic network within a city good or bad.

First, I put down some bus stops in one of the larger towns, placing them near the most dense residential/industrial/commercial/leisure areas and it was an immediate success. Then I tried the same in one of the other large towns and hardly any people use it. Then I aded quite a few more stops, which did help but only a little.
After this, thinking geographic extension might be more important (as people have to walk more there) I tried to make a bus line connecting the various parts of a town that's smaller but extended over a larger area, but people don't really use my stagecoaches there, either.

Can someome explain to me how I can know beforehand if it's worth it to build a bus line in a specific town?
I know I can click on people to see where they are headed and on buildings to see where the tenants work, but this also doesn't always help (in all my unsuccessful towns, logically, people should have at least taken the bus to their workplace).

Thanks for the tip - I haven't even considred linear lines so far, but I'll definitely give them a go.