Earlier quoted context omitted.
Because there was nobody who thought about it. We had a similar situation in Russia. A mobile operator was cooperating with government to hack into activists' Telegram accounts. They disabled SMS service for a user and then requested a password restore using SMS, intercepted it and got access. But they forgot to delete this information from their internal systems, so when the user called support, they told them that…
Why wouldn't an intelligence agency just intercept it quietly? If I were sufficiently motivated and had global assets willing to do my bidding I could probably have found a way to intercept it at a sorting facility or en route or by sending in an "inspector" or social engineering or something. Why on earth would they do something so obvious to leave such a paper trail when you know they could pull this off quietly?
The ideal approach would be to have packages of the "interesting" kind automatically diverted to a scanning location, and then continue on their way...
Dont think of it as them being interested in a single package. They are interested in setting up a mechanism by which ALL packages of interest can be diverted with only very small effort on their part.