Look the same on all platforms. Allow artists to create simple animation quickly. run fast. The key selling point of flash was that it was an author once, run anywhere tool. I could use keyframe animation along with a simple scripting language to make almost anything. Not only that it was fast to build and deploy. Nothing I've seen recently allows an artist to do the same. I've tried a couple of times over the years…
This is why I stopped being interested in modern web anymore. Everything is deprecated at unbelievable pace, you can't keep track of it unless you work full time in the field. If it was all for great efficiency and performance, I'd get it, but it seems to just follow the newest fad every 2 years. Maybe with wasm that could change, but I'll believe it when I see it.