Festus,
Although the author of the book doesn't elaborate, my own opinion is because Parker, Elbert, Elizabeth, Eastonville and the like were up and coming farming communities that were not being served by rail. Why build on a route where two competitors are all ready beating each other up?
Another factor may have to do with the fact that both sides of the valley on the way to Pueblo from Denver was occupied by the D&RG and AT&SF and Right-of-Way or easements may have come at a very high price.
I think that Evans was looking for some virgin territory to serve on his way south. The line was twisty and curvy but initially well built, much like the South Park. The problem with the line was that it was in a flood prone drainage basin and that's what eventually killed it.
Just conjecture on my part.
As for the track in Colorado Springs. Not being intimately familiar with Rock Island Mileposts I would assume that this is the track from Powars Blvd. to the Joint Line. I believe that the track from Limon to Elsmere is long gone. This track was operated by the D&RGW until it's merger with UP. After the merger it was put up for bid.
That poor old ex-Rock line from Limon to the Springs has a really checkered history as to owners and operators. Suffice it to say that it's probably in Colorado Springs' best interest to have the line railbanked as things stand.
Rick