How do people calling themselves casual feel about the difficulty level?

[L-D-Omlette]

It's due to the scripted nature of things. The players that know it well find it extremely easy, since you don't know it they label you as bad. The problem isn't the players it's the fact that it's scripted. Poor design causing more unfunness. (hea new word. lol)

Player nature won't change.. but the game sets low expectations by veterans due to its scripted nature.

It absolutely is the players. The fact that there are veterans, few and far between they may be, that are patient and willing to go at something multiple times to help others gain practice stands as evidence to this.

The ones that get mad and quit at the first sign of failure are making a choice, the game is not forcing them to do that. Do I blame them for that choice? No, they have every right to want to get their shinies asap. Having the expectation for everyone to have the same skillset and/or experience as you is just setting yourself up for a bad time. Players shouldn't take it out on others because they have unrealistic expectations.