You know...you can already get analytics if your mirrors just agree to share logs. It may not be as detailed or complete, for sure, but using another analytical tools does feel a little superfluous.
> Is the problem that they are using google's service?
This is part of it I think. The brew devs get stats, but so does Google which they can aggregate across everything. Standing up your own analytics server/cluster, especially for a project the size of brew, wouldn't be trivial and I can see why they leverage Google's service.
But I can understand people not wanting to have data sent to Google. I moved everything off Gmail to my own E-mail server back in 2013 and moved search to DuckDuckGo.