Not implying at all that it isn't developed -- back in the early 00s this was the only way we could do tracking largely. But Google Analytics is completely blind when you block it, and that's a huge percentage of the market. For example, simply loading a 1px image (the old way of doing a lot of server-side tracking, and still the state-of-the-art way of doing email tracking) is insufficient when the client is hard blocking the ad server. In that scenario the only way to do it is server-side at the actual web server serving the web page (not some third party ad server), and most large analytics services don't offer anything like that anymore.