Of the more than 100 Class I railroads that existed in 1960, only seven survive today. The definition of the minimum revenues necessary to be considered class I has changed, but even after adjusting for inflation only ten would exist today. This document describes some of the early attempts at mergers that led to this reduction in railroad companies.
The Western Pacific paralleled the Southern Pacific for its entire length, so SP acquisition of the WP would reduce competition. Rather than let that happen, Santa Fe stepped in to be a white knight. An SF-WP merger would have made more sense as WP and Santa Fe exchanged north-south traffic and Santa Fe didn’t compete with WP on its Oakland-Salt Lake City route. When the SP-WP merger was rejected, Santa Fe stopped its effort to acquire WP.
Unfortunately, when Union Pacific acquired Western Pacific in 1981 and then Southern Pacific in 1996, the competition in the Oakland-Salt Lake corridor was lost. Since Southern Pacific had previously merged with the Rio Grande, competition between Denver and Salt Lake was also weakened. This may be the most important corridor in America with such limited competition. So it probably would have been better if Santa Fe had followed through and purchased the WP in the early 1960s.