Because congress represents lobbyist interest and not the interests of their constituents. It's not a democracy, it's not a republic. It's an oligarchy or corporatocracy. That's the joke. It's just that the mob is the few people who have most of the money.

A mob at least doesn't pretend to care about whomever it's bullying. The senate whose majority represents a minority has to make all sorts of contortions to act like they're doing the right thing, because they have to both justify what they're doing and their right to do it.

I think the US founding fathers somehow thought the senate would be populated by people who could put some sort of "good of the nation" ahead of their own interests.

The senate was originally elected by the states directly, the general population didn’t play any part of the process. This was abolished, in addition to many responsibilities of the senate - oversight of the executive, a leading voice in international relations - have been ceded to the executive branch. I wouldn’t say it’s more of a joke than mob rule, but it’s a thin veneer of respectability.