The failure is forced on them when and if they attempt harder content. A gigacasual hops into EX and all of a sudden finds themselves on a completely different playground, and this still isn't anywhere close to the game's most difficult content. When you boil down posts such as yours, it is very easy to discern that you want more difficult content to be forced onto the casuals. What happens then is you will really have a problem on your hands because the content you can now sleep through can't be cleared.
Players who want to learn will do so on their own accord. And the players that want to learn typically want to attempt more difficult content. Even for something like EX, the concepts behind things like Crit/DH and optimization of skills still aren't that important because in order to clear content at this level, what is more important is group coordination and understanding mechanics along with not failing them. Players who want to go above and beyond will make the effort to understand PvE inside and out.
For the casuals, the game only needs the players to understand how the game is played. Things like MSQ progression, job roles, light parties require 4 players comprised of tank, healer, and 2 DPS. Full parties are double of each; some duties require a min ilevel, hotbar/crossbar/hotkey allocation, abilities/spells/weapon skills, etc. There are tooltips for nearly everything, and the menu also has a help log. Whether or not a casual players actually looks at it is irrelevant. These tools are still available to them nonetheless. Content lower than EX and the very occasional NM duty where the devs will ramp up the difficulty a bit shouldn't matter much to you. If you want more challenging content where players are required to know more and try harder, I suggest sticking to more difficult duties.
