Well, unfortunately I don't seem to get notified of comments on the wiki pages, otherwise I would have answered...

I did post an answer out there, but to summarize...

Our Piwik server is an internal resource and is not exposed on the net. We could not do client side tracking w/o exposing the Piwik server, which we don't want to do.

Doing server-side tracking, we can keep our Piwik server hidden from the world and still gather the metrics we need.

Do you know here the page was moved?

I believe that the old Wiki is gone - but courtesy of the wayback machine: Here you are. You judge if it's still applicable today - it's from the 6.1 times.

Note that the original post is quite old...

First, Liferay added support for Piwik directly into 7.0 (might have been in an earlier version, I don't remember).

Second, Piwik changed its name to https://matomo.org but, even though there is a name change, I think the crux of the details are likely still going to be the same.