Everyone spies on everyone. Why wouldn't you? America just happens to have some of the best technology to serve that purpose. This spying was revealed by a third party though, which is different.
If I was a country, I wouldn't announce to others I had learned about their spying for 2 reasons: I can no longer feed false or useless information through that channel. If they move on from that channel, they will be spying some other way now, a way that I don't know what it is. Merely publicizing the fact we caught them does not change why they were spying on us in the first place, and they will continue.
Secondly, they may also be aware of our own espionage activities, and have kept quiet about them. If we burn them in public, they will burn us too - so there's an element of mutually assured bad press. Because this was revealed by a third party though, that mitigates #2, allowing the people spied on to publicly complain, and #1 is irrelevant by then.