The problem isn't so much with WebGL performance. WebGL is easily fast enough for simple particles like this (although 2D canvas could probably also manage it). The problem is that a lot of web devs don't have a full understanding of the OpenGL pipeline, and how using tools and effects in one way rather than another can lead to crippling performance issues. That entire scene could probably be batched into a single render call.

WebGL has lots of potential to be lightweight and non-intrusive. I've started writing a series on the topic to try and dispel some myths of WebGL being slow and bloated.

https://medium.com/p/abf669857722

Part 1 of the technical aspects: https://medium.com/p/cebd176c281d