Jd Smith1
Hero
Motivation is never a problem. Tie XP, at least in part, to job performance, and it works perfectly. In non-fantasy games, I always use employment as the party rationale.Look for an inciting event that kicks off the moving parts in the setting. Maybe an election in a jurisdiction that the railroad is getting close to.
In cases where the party is employed, too, it can be difficult to drive the job's purpose as a character motivation. Especially when, in the idealized west, there are more interesting ways to make a living than breaking strikes (I hope you have a mature group, willing to tackle the racial and socioeconomic issues you've identified in search of a fun experience).
I only run historical, rather than idealized. Much better fodder for scenarios by drawing from history.
My players have been with me for years, all hand-picked and carefully screened. That's not an issue.