You kind of do though. [1] The government sends national security letters to tech companies all the time. Interest in certain topics can land you on lists. [2] The US absolutely intercepts anything they can in plain text (and does their best to break the encryption on things that aren't).

1. https://www.zdnet.com/article/top-374-keywords-the-u-s-gover...

2. https://en.wikipedia.org/wiki/XKeyscore