JS has been in front-line for these functionalty, and HTML has been dog-slow to catch up with slow standardization (not based on usage more academical) and recommendations.
HTML can do that. yes. but adoption? welp, I don't really care nor will I use it unless I have to. I will use whatever was available in practice and continue to use them.
Odd to both complain about adoption and out yourself as someone unwilling to move to a better solution because it’s less familiar. What do you expect the answer to be here?
I suspect he's still optimizing for IE5 compatibility.