John is equally disappointed because he thinks that by exposing his children to the farm labor he couldn't wait to get away from, they'll finally admit that they're freeloading off of him and, since they insist on acting and thinking on their own instead of when a smirking pile of ordure with a train fetish wills it, are horrible and ungrateful children. To them, it looks like they're being singled out for punishment because they exist and are expected to state "I really am a horrible child for having free will and should pay you back every cent you ever spent on me with interest as penance. I appreciate being called a parasite and want more verbal floggings."
The end result of all of this is to drive home a lesson that Elly and John didn't intend to teach. It teaches the kids that John and Elly don't give a brass razoo what they think and hate the idea of doing so. Too bad that they've been so crippled by John and Elly's selfishness that they need to be parented.