- search history of more than 3 months ago is somewhat worthless for analytics/advertisement purposes;
- search history of more than 18 months ago is really worthless, but hey, we can also keep those just because we can.
This is meant to be PR statements to try and prepare for increased scrutiny and data privacy they see on the horizon.
This is, imo, meant to be a way for them to tell the masses "look we automatically delete you data!", expecting them to not have any understanding of models that can be built from the underlying data.
Unfortunately, the tech press will cover this at face value praising Google, as their livlihoods are all dependent on Google Ads / YT and free services like AMP.
https://myactivity.google.com/myactivity It's on the hamburger menu