I wrote SVG-SMIL export for Animatron (www.animatron.com) in 2015 that aimed to get near the level of Adobe Flash in plain browser, however it was extremely difficult due to broken SVG-SMIL implementations in all major browsers. You can see some examples here:
The issue back then was that Google suddenly announced their intent to deprecate and remove SVG-SMIL from Chrome, instantly freezing all development there. However YouTube complained and made them change their minds; later they put it into a "frozen" mode but didn't remove it.
For most artists it would have been a risky bet to use it if Google didn't want to support it any further, despite the promise of having an official standard for animation in all browsers.
https://drive.google.com/drive/folders/14DKPte-1YvU5IV3Rb8zd...
The issue back then was that Google suddenly announced their intent to deprecate and remove SVG-SMIL from Chrome, instantly freezing all development there. However YouTube complained and made them change their minds; later they put it into a "frozen" mode but didn't remove it.
For most artists it would have been a risky bet to use it if Google didn't want to support it any further, despite the promise of having an official standard for animation in all browsers.