When any and all of us step up to the door to a quest, we make a choice on what we are going to do for ourselves. Challenge, loot, exp, etc. Casualization is a term that has no realistic meaning in an environment where personal choices for gain are made.
Casual to one player is difficult to another. Or Casual to one player is fitting risk vs reward for another.
You want incentive to run harder difficulties? More exp and higher chance at loot isn't enough for you? Then that means you are hitting that threshold of risk vs reward. And that is also why lower difficulties are 'easier' less risk, less reward. It ultimately becomes a balancing act: what are you willing to do for that shiny.
Now, onto what I think would push people to do EE more often despite the risk.
More loot chances. My biggest cases: Amrath and Shroud.
Yes, their loot has been passed by. Level 28 loot does that. Regardless, as soon as Hard and Elite got more chests with each chest offering another chance at that same loot; lfms and runs all over the place for it.
Would this saturate the market with items? Maybe. When the drop rate is 1 in 300+, then you can afford to drop an extra chest here and there on elite difficulties.