Earlier quoted context omitted.
People yes. Corporations no.
What is a corporation but people? Companies are groups of people. They're one or more owners, some managers, possibly some staff. If you take away all the people, then there's nothing there.
A corporation having contribution rights multiplies the otherwise imposed contribution limits on the underlying humans.
A corporation allows tax planning opportunities not afforded to the bottom 90-ish percent of the country (such as shifting income to alternate years to avoid progressive taxation, and utilizing expenses to lower that income in ways a W2 cannot)
Corporations are granted benefits that people do not get, and CU disturbs the balance of power.