Most people dont vote in primaries. That is only time choice is really an option for same party candidates. Since CU basically makes bribery legal its that much harder to remove bad incumbants since they have more campaign funds.
If they'd decided the alternative, then any 501(c) organization could find itself muzzled during election season (which is roughly 90% of the year at this point). This include organizations like: EFF, ACLU, and Planned Parenthood. All of these are technically corporations.