ICANN actually does work on this. I'm not quite sure why. ICANN's ability is quite limited, of course, since noone's required to accept ICANN's PRs or do as ICANN requests.
Prepending https:// has issues. One, it's a matter of telling the general public what to do. You might as well blow against the wind. Two, this applies to IDNs, which are generally used by people with different keyboard layouts. If you have a 'ت' key on your keyboard, you'll have to switch keyboard layouts twice in order to input 'h'. Telling people to do that really is blowing against the wind.