This might be partially a fashion thing: people want the flashy interactions less. I for one appreciate some boring text with minimal animation! Also away from games where animated interaction is part of the point, designing a good animation that works better than text+images is often not as easy as many think, and you need to contend with that before you attempt to implement the design.

As there are less people wanting to make the animations the tools that would have replaced the tooling for flash (but outputting SVG+JS instead), of which there were a fair few in active development at one point, have languished unloved and incomplete – so not only do fewer people want to make such animations but those that do want to don't have easy tooling to do so.

There are a couple of e-learning sites out there using interactive animations to illustrate their points, one often has sponsor spots on a couple of podcasts & video series I follow though I forget its name ATM. I wonder what tooling they use, if any (though I doubt it is all manually coded).