The issue of poor bus ridership has various causes, there is no single major reason for this issue.

Example:

A) Poor bus frequency, either caused by human factor or simply there is no dedicated bus lane
B) Poor urban development which contributes to less convenient access to bus shelter

I think if bus servce is frequent, predictable and has priority over automobile traffic at traffic light, maybe this would improve experience for bus commuters and consequently, more would be tempted to take bus.