When you're running a proprietary video service that's supported by ads and analytics, there aren't that many "legitimate traffic inspection cases". Google pref

When you're running a proprietary video service that's supported by ads and analytics, there aren't that many "legitimate traffic inspection cases". Google prefers people not to mess with their network traffic and would also prefer it to be a bit harder to write YouTube downloader scripts. From a user perspective, you'd want to break all TLS connections and sniff every bit of data on your network, but that's not the perspective Google has when developing their code. Signing data is just duplicating TLS security measures with a second key. TLS already signs the data, Google just needs to verify the root of trust.