fairy okay is the key word.

Everything works fairly okay on modern hardware. I'm sure someone could build a 3d rendering engine using only table elements and css and it would run decently well.

There are hundreds of tools in the belt, people can use any of them to tighten down the screw, but it doesn't mean that they are the most efficient or best to use.

I would also say that a lot of web games are closer to documents than you think. A chess board could be seen as a document, it has tables and rows, the characters are just shaped different than the characters we write with.

Something like a racing sim again could be implemented in css but someone who actually understands how to use canvas is going to have a more efficient way to represent it.