It's neither sudden nor backhanded — if either of those characterizations were accurate, we'd have learned about it from something shipping. Announcing it publicly before implementing anything and having a number of privacy protections built-in suggests neither is a fair description.

Reading through the use-cases at https://research.swtch.com/telemetry-uses one thing to consider is that these are the kinds of things people care about as a project matures — once you have a large number of people depending on your project, you have to worry more about unintended consequences as you evolve and since the user community has grown larger and the project more stable it's also harder to know whether the people you hear from regularly are representative. When a project is small or mostly used by enthusiasts you can be more confident that your understanding of what people are doing is relatively accurate but that just isn't true over time. For example, how many millions of Java developers never contact Oracle or the OpenJDK developers throughout their entire careers?