Earlier quoted context omitted.
To be fair, look at it from totally the opposite direction to see their point of view. Your workers are under threat from poorly made postal bombs that could easily blow up during processing, killing your workers. Due to the vast volume of post you process, the threat is real and non-trivial. Do you do nothing? I think you obviously have to do something, whether you go as far as they did is what's up for debate.
Yes, when will the USPS do something about the 0 postal workers killed from letter bombs this year, last year, the year before last, the year before last before last year, ...? More of them are endangered by their shitbox LLV trucks catching on fire.
For example, look at this[0]. Two people physically attacked a postal worker after accusing her of "stealing their stimulus checks"[1].
Sure, you can say that this case had nothing to do with USPS surveillance. But it just goes to show that there are plenty of serious dangers to postal workers other than just nigh-non-existent "bomb in the mail" scenarios that you seem to be fixating on.
0. https://www.kiro7.com/news/trending/police-make-arrest-after...
1. https://news.yahoo.com/usps-worker-beaten-michigan-alleged-1...