Allowing Google to run an ad campaign targeting their members wasn’t the benefit Blue Cross was talking about, that’s a side effect from them not turning off the data sharing option in the Google analytics settings.
The analytics data is used for prioritizing development work. If a tool they have on the website relies on a library that isn’t compatible with a new version of React, for instance, do they know how many people use it? Having analytics allows you to decide what’s worth spending the development time to maintain.
It’s a common thing in programming. There’s some legacy code that isn’t being used and yet removing it causes things to break. Nobody has the time to figure out what is still referencing that code, so it just gets a comment next to it saying “Not used, but removing it breaks the build” and then forgotten about.