Coleman:

Try running a business sometime; you'll soon understand that the realities that UP and other railroads (and any other business, for that matter) are far different from what railfans like us and other outsiders perceive. What may seem simple and common-sense to you or me may in fact be impractical, inefficient, and far too expensive in the long run to even consider, much less implement.

Sure, as a railfan I'd love to see the Rio Grande Southern and the other missing parts of Colorado's Narrow Gauge Circle restored, but who's gonna pay for it? And how? And what could those lines possibly haul to remain profitable? Most of those lines were built to tap the mineral wealth of southwestern Colorado and as part of the original mainline to Utah; when the silver market crashed, the other mines played out, and the mainline was rerouted, most of those lines no longer had a purpose and were removed, and the construction of paved highways and the resulting influx of commercial trucks like the ones you drive made the remainder obsolete. Tourist traffic has kept the Silverton Branch (as today's D&SNG) and the remaining segment of the line from Antonito to Durango (as the Cumbres & Toltec Scenic Railroad) going, but those lines run through remote or hard-to-reach scenic areas with few or no roads; the rest of the Circle, on the other hand, is easily accesible by car and much of it isn't as scenic (it's still a nice drive, but it's nothing compared to Animas Canyon or Toltec Gorge.)

The Modoc line is no different; it was a viable and useful route when it was built, but that was no longer the case by the time it was finally abandoned. Even if SP had stayed out of Philip Anschtuz's cluches and remained independent till today, it's quite likely that its managenment would've chosen to ditch the Modoc for the very same reasons as UP.