But as far back as the 1960s it became so politicized that the writing was on the wall what would eventually happen...
Currently politics aren't really a problem ~ in fact, it has more to do with the Great Obama Recession which never really ended. Secondarily it's a question of technological transformation where increased mechanization, automation, computerization, robotics and improved work methods have served to incease productivity to phenomenal levels.
Ordinarily growth in mail volume would have kept up with productivity improvement and minimized the need to cut personnel. When mail volume growth stopped productivity improvements didn't. Now they need to cut personnel.