Adobe Flash/Animate provided a best-in-class animation and vector art package that still has little competition. Animate can actually export to HTML5, but they didn't bother using the SVG/SMIL animation model. Instead, they pre-render everything as a series of spritesheets and render them to a canvas.
I can see why they did this - the SVG and canvas vector rendering models are different enough to make blindly rendering SWF content to it cause rendering artifacts. (It's one of our biggest longstanding bugs in Ruffle - canvas masks just look weird.) However, Adobe could have ameliorated this either in the exporter, the authoring environment, or by pushing for Flash-style mask options in web standards that deal with vector rendering. Instead, they went with the far worse but quicker option of prerendering so they could say "hey we totally do HTML5 now".