That, plus:

* Echarts is about the only dependency in our project that I can upgrade - and be sure it never breaks anything. It is so well-thought in that regard. Upgrading for 3.x to 5.x? Sure! "npm update" and everything just keeps working smoothly. That is so refreshing to see these days. Unbelievable.

* It's both SSR-friendly and SPA-friendly. Being mostly vanilla-js, works seamlessly with both react/vue/apline AND with old-school rails/asp.net/php/whatever. Our app is pretty classic SSR (https://www.jitbit.com/) and I can construct my chart's JSON object on a server using some linq-queries and provide that to echarts.

* ...OR I can give it a reactive object from vue-based SPA. Dun matter, it just works.

* whenever we have to add some workarounds (like, showing hovering labels on a pie chart with a bold percentages or something) - I never have to dig into their sources. Almost anything has already been figured out. Easily googlable and "LLM-able".