My reason is the server not being able to handle the traffic. We used Piwik but I couldn't trust it'd be able to handle big eventual spikes of traffic (which th

My reason is the server not being able to handle the traffic. We used Piwik but I couldn't trust it'd be able to handle big eventual spikes of traffic (which the site itself could, being static and on a CDN) or that it wouldn't slow the site down (if I remember correctly I had the option to call piwik asynchronously and not slow down the site, but at risk that it'd be less accurate if people closed the window / navigated to another page quickly.). Of course you can run your own analytics on AWS or similar and have no issues with handling traffic, but that means higher costs / difficulty in setting up and maintaining it.