I think it's fair that GA is free and Google gets some benefits from using the data for their ad network.
https://github.com/th0th/poeticmetric
Looks interesting but haven't delved in it too much. I do like how I can create specific analytic tracking events without worrying too much about ad blockers but that's hardly unique to Umami.
There's also another interesting analytics open source project whose name I am forgetting. It was written in C or something and was efficient enough to allow free usage or self hosted, it was a simple hit counter I believe.
In my case, my motivation was that I want to use LLMs to query the data with agents. This whole thing was surprisingly easy to setup and a positive thing is that you don't have a scary extra data controller doing shady things with the data.
Matomo charges 22 euros for 50k hits/month.[0] Basically, it's unusable for anything other than a hobby site - especially with the number of crawlers nowadays.
If you self host for free, you're missing basically all of the good parts of web analytics such as funnel analysis as they lock all of those features being paid subs.
[0]https://matomo.org/pricing/