Its the last remnant of the various property owning/landed gentry/aristocracy control of government. They had to give up their exclusive right to sit in court and then “democratic” government, and then their exclusive right to vote.

They are holding on to money-as-influence, trying to convince us its fair because everyone can make donations (you get a great tax receipt!!). However, even donation limits are mainly just a way to cover up their thumbs on the scale, because all they require the rich to do is spread out their money.