> according to piwik my website had 23% more visitors than on GA

A fair share of that is probably because GA is much better at identifying the same user across multiple browsers / devices. If they identify two browsers as the same person on site A, they can know they're the same person on site B, even if site B on its own doesn't have enough to figure it out (so piwik can't know it).

or because GA is a well-known static target for blocking.

10 years later and still no PostgreSQL support.

Also no support for ELK and plain-text-folder-managed data structure, so what? do one thing and do it well.

I think one of the things that GA is doing is actively removing bots visits because they skew country/browser/etc. data. Maybe Matomo is not doing that (so well)? Another thing is that people blocking GA trackers will also not show up in GA, but will (probably) show up Matomo.