Comment by flomo
Just some blatantly obvious examples: Select Multiple was some Windows 3 garbage, and HTML didn't have a 'combobox', much less a 'multi-combobox'. (MDN says datalist is not supported on Firefox, so maybe it still doesn't.) So write it yourself, or use a library. The form validation stuff is still bad, and idk if modern desktop browsers have a good date control.
I can agree that it is bad. And there might be some examples where <select multiple> is the "best" way, but I cannot ever remember a real-world use case where it was not better solved using a list of <input type=checkbox> anyway.