It is always sad to hear of lines being taken out. Once gone they are not coming back. As for the why they are gone, well a lot of things contribute to their demise.
When deregulation came I suspect the RRs did not have a vision of continuation on many of these branches to begin with. As their costs/rates went up, I suspect upper level managers at the RRs and the shippers were not proactive in considering the future of the lines. We all know in the case of lines near the Columbia River truck/barge rates were very low; tough to compete with publicly funded transportation! The local shippers did not have unit train loading to any extent and the rates for 1-3-10 car moves were not favorable. Common (short term) sense and economics at that time began to kill off the branches. The RRs did not respond well to this situation for a variety of reasons, local shippers were short sighted, and local governments were slow learners too.

In all, I think the RRs, and shippers all share blame in loosing these branch lines.