These are close, close allies though. We aren't talking about North Korea. We are talking about countries who have deep diplomatic and military ties.
The reason why you wouldn't do something like this, is because there was a damn good chance that it would leak out, mortally wounding your relationship with these people.
Secondly, the utility of this particular SIGINT program is highly questionable. What is the ROI on something like this? Germany is not plotting against the United States. What scenario would they use info for?
That's not how alliances and trust work. In this context, suspicion is a form of accusation - and it is wholly inappropriate and wrongful for the US to accuse Germany or France of plotting against it's national security interests.
Otoh, what this establishes is that in fact, the US is quite willing to consider actions that may damage the national security interests of its allies.
In short, this sort of spying is a significant disruptor of any sort of lasting trust between nations. If everyone behaves like the US, there are no "allies", only temporarily convenient partners who may be betrayed at any point.
> Otoh, what this establishes is that in fact, the US is quite willing to consider actions that may damage the national security interests of its allies.
That's long since been established. Hell, the Pentagon has plans for an invasion of Canada.
The US doesn't need to spy on the German chancellor to be certain of this. There is no conceivable plot that Germany could be involved in that could damage the US, and both countries know this. Same with the UK, Israel, France, etc.
The EU doesn't import US beef because of banned chemicals used to raise US cows. Imagine if the EU implemented more stringent requirements on, say, GM foods. Or other livestock. Banned the pesticides used in California Oranges, etc.
Trade agreements, tariffs, standards and sanctions - there are many ways for European countries to damage the US economically.
Economic espionage, sabotaging foreign trade talks which aren't judged to be in the interests of the US, gaining the upper hand in negotiations. The potential utility of this sort of SIGINT is high, if you are willing to engage in amoral behaviour on a massive scale, treating allies as enemies.
So the question it raises is, why were they collecting this information? You can be sure they would not collect it for no reason.
The reason why you wouldn't do something like this, is because there was a damn good chance that it would leak out, mortally wounding your relationship with these people.
Secondly, the utility of this particular SIGINT program is highly questionable. What is the ROI on something like this? Germany is not plotting against the United States. What scenario would they use info for?