The underlying problem with "nobility" is that when they "help the poor", they end up making them an "other" that relies on them. They get so prideful about helping people, that they would avoid actions which are best for helping people the most if the actions undermine their authority over them.
An example would be education. The best way to help people would be to give all people access to education, but the high class people would assume that the commoners aren't able to learn as well as they are able to. They would prevent social mobility because they want to help commoners while not hurting their own standing as lords.