And the vast majority of player will run the casual mode only. If there is an easy route, most people will take it.
You’re idea is basically the normal/ruthless modes from POE. afaik GGG never announce anything about how much poeple play each, but someone did it on reddit a while ago with a fair amount of extrapolation (https://www.reddit.com/r/pathofexile/comments/160oewa/why_is_ruthless_a_thing_at_all_with_numbers/). He conclude that ruthless player is less than 2% of the entire playerbase.
Adding that ruthless mode is apparently a pet project from top management at GGG (which really help it to be a thing), why would Blizzard invest some time into a similar mode that may be barely played ?