The city's bike-share program lost money in each of its first three years of operation. ______, ridership had grown enough by the fourth…

The passage describes an initial period of financial loss followed by an eventual, contrasting turnaround. Nevertheless signals exactly that kind of contrast: despite the rough early years, self-sufficiency followed. By contrast typically sets up a direct comparison between two separate things existing simultaneously, instead of a single program's own change over time. Namely introduces a specific example of something just named, which doesn't fit this shift between two time periods. In particular would frame the second sentence as a more specific instance of the first's claim, not a reversal of it.