It starts when transportation planners get the "bright idea" to cancel lines that don't have some threshold of number of riders. On paper that looks good because it culls the lines that aren't as profitable, allowing the operating budget to shrink. In reality, it makes transit slightly less attractive, less flexible to riders, and it means that some places aren't reachable directly, conveniently or at all.

Decades of this kind of behavior coupled with increasing distaste for public expenditures and you're left with a transit system that only serves patrons whose time is worth almost nothing, who are desperate enough to burn 1-2 hours of travel to get to places that are reachable in 20 minutes by private vehicles.